The cast of Steins;Gate is notably fairly minimalistic: There are only the eight lab members, the Tennouji family that Okabe rents from and a few rarely appearing family members such as Ruka's father. Names are in Japanese order (Family name first, given name second).
Labmem 001 and the protagonist, an 18-year-old 1st-year college student and leader of the Future Gadget Laboratory. Around a decade ago, in order to help Mayuri through a difficult situation he began styling himself as an evil mad scientist, exasperating others with his chuunibyou antics. Despite his goofiness, he's actually pretty intelligent and has an intuitive grasp of much of what they're doing. He retains his memories when the past changes with complete clarity, an ability he calls the Reading Steiner.
Subverted horribly in the Gamma timeline where he is physically fitter, richer and more disciplined but this is a result of him willingly joining SERN as a Rounder, spy and researcher.
Always Save the Girl: When the choice between saving Mayuri or saving Kurisu comes up, he admits that he honestly doesn't care that the latter involves allowing the world to remain with SERN's dystopia. After making his choice, in the True Ending he's also completely unconcerned with the fact that the future he's heading towards results in the near extinction of the human race. He's not going to allow Mayuri to die to save billions of people he doesn't know.
Amnesiac Lover: In the Faris ending, Okabe's meddling with time results in a world line where he knows none of his friends except for her, who he's been in a long-term relationship with. Of course, since Reading Steiner only lets him remember his experiences on the previous world line, he has no recollection of this. While this distresses Faris once she realizes he isn't play-acting as usual, they do agree to work towards starting a new relationship.
Awesome McCoolname: His 'true name' of Hououin Kyouma is supposed to be ridiculously cool, though the point is that anyone over fourteen would giggle to hear it. The characters forming it mean Phoenix Temple Madness of Truth.
Badass Labcoat: Deliberately attempts to invoke this trope with his wardrobe choices. Sometimes it even works. He's particularly thrilled when Kurisu starts wearing the one he bought for Daru that went unused.
Be Yourself: During Ruka and Faris' routes he upsets them by acting more normal than usual. When he acts like the person they know, they're much happier and he's much less stressed out. Kurisu, in a different take, appreciates it most when he acts like Okabe Rintarou and will flat out ask him his opinion as Okabe and not Hououin, though the opinions are generally identical.
Big Brother Instinct: As Okabe admits early on, he basically adopted the Hououin Kyouma personality because he was worried about how flighty Mayuri is.
Break Them by Talking: In the final arc before the True End begins, Okabe has to undo the last D-mail, the one that Moeka sent. However, he doesn't know what mail he needs to send to do it. To get that information, he forces Moeka to break by telling her how blatantly she's been abandoned in a way she can't fully deny. Oddly enough, though, this actually ends up being better for her psychologically. Until she gets killed anyway, that is.
Catch Phrase: "This is the choice of Stein's Gate!", "El Psy Congroo", among others.
Character Development: He starts out a somewhat tsundere dork, but around the 13th he has to start growing up and becomes by turns rather clinical, depressed and frantic. By the very end he's found a happy (well, sort of) medium between these two points.
Despair Event Horizon: Breaks down crying after countless failed time-leaps in order to save Mayuri and is in such a state of desperation that he actually attempts suicide. Of course, You Can't Fight Fate, and Mayuri's relief after saving him and finally being 'useful' only sends him further into despair.
The Determinator: He keeps putting himself through hell to save Mayuri, made worse by the fact that all the damage he does is known only by him. He keeps it together until he has to sacrifice Kurisu to save Mayuri at which he grinds to a halt and completes his breakdown.
Freak Out: After the 13th, his personality takes a sharp and unhealthy turn for the worse as he struggles to avert Mayuri's death. After everything is said and done, he doesn't quite go back to normal, but he gets close. Depending on your ending, that is.
Forceful Kiss: In order to stop Moeka from screaming for help he forcefully kisses her until she gives up.
Future Badass: In the future Alpha timeline, he leads an international terrorist group against SERN. In the Beta timeline, he creates an advanced version of the original Alpha timeline time machine.
The Gadfly: He loves picking on Kurisu, usually by using nicknames that he knows she hates.
Geek Physique: Okabe is skinny and unathletic. Even climbing up a few staircases is enough to exhaust him.
Gratuitous English: Styles himself a Mad Scientist following the Steins;Gate's choice. Kurisu notes in utter disbelief that the latter is actually half German.
The Heckler: Attends Dr. Nakabachi's and Kurisu's speeches at the beginning of the story and upon hearing something he doesn't like instantly begins heckling them. The difference between the two is obvious: His objections to the former are completely valid and is nearly escorted out before Kurisu pulls him aside, and the latter knows exactly what she's talking about, stops someone from removing him and turns it back around on him to make him look like a complete fool.
Historical Villain Upgrade: In universe: In one future timeline he's known as a terrorist against the SERN regime. It's even true, but the terrorists are basically the good guys.
He complains about how everyone calls him Okabe or Okarin instead of Hououin Kyouma like he'd prefer, but there's essentially nobody he calls by their proper names. He calls Kurisu in particular about half a dozen things that all irritate her rather than her actual name.
After Okabe begins heckling her during the seminar, she quickly recovers and then addresses all stupid questions and reasons why time travel won't work to him directly. He thinks it's really rude and gets defensive.
Improbably High IQ: Okabe claims to have an IQ of a possible but very unlikely 170 - whether he's just making it up or not is up for debate.
He's emotionally dense and can piss people off even when he's not trying to, such as picking at Kurisu's statement about how she hasn't seen her father in years.
If you skip one of Mayuri’s phone calls, he goes and talks to Moeka instead. Irritated at her sending him mails instead of talking even when face to face, he finally realizes that she’s too socially awkward to speak, though he chalks it up to being scared of a super mad scientist specifically.
In-Series Nickname: Refers to himself as "Hououin Kyouma". Mayuri and Daru call him "Okarin".
Jerk with a Heart of Gold: He likes to act hammy and 'evil' and bickers constantly with Kurisu and Faris, though the latter doesn't seem aware that that's how he views the situation. However, he's actually pretty concerned about Mayuri and Kurisu and even forgives Moeka for murdering Mayuri after he understands the situation a little better.
Large Ham: When he's acting out his Hououin Kyouma persona he tends to be very loud and theatrical. When Okabe himself shines through, he's inclined towards gloominess and is actually fairly mellow.
Last Name Basis: His given name, Rintarou, is almost never spoken by anyone. Daru and Mayuri call him Okarin and Faris calls him Kyouma, but not even the impolite Kurisu uses his real name.
Let Them Die Happy: In Mayuri and Kurisu's ending he forgives Moeka so that she can die in peace. Even after this is inevitably undone by the course of the plot, he still keeps his word. She's even invited to the club in the epilogue.
Like Brother and Sister: He views Mayuri as a little sister figure, though Mayuri herself seems to hover somewhere between utter devotion and a crush.
Living Emotional Crutch: Mayuri is very dependent on Okabe after the death of her grandmother, but is beginning to feel like she's a burden on him. She also fails to realize that she's genuinely important to him and not just a thing to be taken care of. While this is mostly a worry of Mayuri's, very early on it does occur to him that perhaps the mad scientist game has kept her from growing up. Not that he'd say it in those terms, though.
Loophole Abuse: The most notable example is him deceiving his past self using a clever loophole devised by his future self.
Mad Scientist: He views himself as a great mad scientist, the scope of which is basically renting out a tiny apartment, calling it a lab and using it as a clubroom where he occasionally builds weird gadgets.
Mr. Imagination: Styles himself as a great and evil mad scientist fighting against a vague but presumably evil Organization. Mayuri isn't his friend, she's his hostage. And absolutely everything must be named in a foreign language or it just wouldn't feel right. His inner monologue admits that it's all a load of crap, but whatever, he's having fun.
The Nicknamer: Enjoys giving other people nicknames based on their deeds, except Mayuri, who already coined her own nickname "Mayushii☆" and Faris, who doesn't use her real name anyway.
Daru's real name is Itaru, though it's rarely mentioned apart from when the origin of 'John Titor' is discussed to be based upon a multilingual pun by translating his name into English.
Kurisu gets the most nicknames: The Zombie for apparently coming back to life, Christina just to annoy her by getting her name almost right, Assistant to inflate his own ego as a Mad Scientist and a handful of others like Celeb Seventeen. Eventually he admits that he's too nervous to actually use her name.
Moeka is Shining Finger thanks to her ridiculous typing speed.
Ruka is Rukako, which is putting a feminine ending on an ambiguous name that belongs to a feminine boy.
Suzuha becomes the Working Warrior after she irritably tells Mr. Braun that she's a warrior, apparently unaware that this makes her stand out juuuust a little.
Mr. Braun is itself yet another nickname to the landlord, Tennouji. His daughter Nae becomes Sister Braun. Nae doesn't really get why Okabe calls her father that.
Obfuscating Insanity: When the plot takes a turn for the depressing, Okabe occasionally hides his true thoughts, goals and emotions by using his mad scientist schtick.
Oblivious to Love: He's pretty dense when it comes to others feelings and love isn't an exception. Faris and Ruka are unable to get through to him without being really blunt about it. The latter came as a particular shock, causing quite a crash.
Politeness Judo: Not wanting to carry a heavy computer back to the clubroom and hearing Kurisu's refusal to help, he gestures to Ruka to get him to offer to help. Once Ruka does, he politely refuses and says he'll do it all on his own while Ruka repeats his offer until Kurisu hesitantly offers to help out too, at which point Okabe instantly agrees, much to her surprise and irritation.
Though deep down he's not serious, eventually he really is being monitored by an evil organization. One that assassinates his best friend followed by kidnapping and enslaving his love interest, forcing her to work on time travel for them.
At the beginning, Okabe wonders if the woman trying to get people back to the conference is trying to cover up the apparent satellite. It’s beta line Suzuha, though this doesn’t become clear until much later. Okabe himself is in there with her.
Proud to Be a Geek: Okabe makes no effort to hide his questionable hobbies and passion for bizarre scientific endeavors. In fact, he plays them up in an effort to hide his true, socially awkward self.
Ret Gone: In the movie, the side effects of his time traveling begin to catch up with him.
Sadistic Choice: Fate gives him one towards the end of the series, when he's forced to choose between condemning Kurisu or Mayuri to death. Thankfully, a third option presents itself, but only after he's been forced to make the choice once.
Sanity Slippage: In the ending for Amane Suzuha his mind starts to run ragged from the sheer repetition and only Amane herself agreeing on a way out helps him. He goes from rescuing Daru from a truck to simply observing Daru nearly get run over with an intense level of indifference to contemplating incredible abuses with just a few repetitions, which horrifies him.
After he and Kurisu finishing lugging a heavy computer back to the lab, he inwardly complains about how often she asked to take breaks and then out loud complains about her, after which she retorts that he asked to rest five times himself.
More seriously, when Moeka first assaults the lab and kills Mayuri he notices that she's upset, hesitant and shaking. As time goes on he slowly forgets this until in chapter 8 he remembers her being completely calm. Moeka is never like that so presumably he's just trying to vilify her in his head in case he has to kill her.
She Is Not My Girlfriend: A lot of people think he's dating Mayuri. Mayuri seems indifferent, but Okabe will correct people. She's his little sister and something to protect, not his girlfriend.
Shoot the Dog: When having to fix events so that Mayuri doesn't die he has to undo the happiness these events brought. Usually right in front of the person in question, who know what he's doing. He has to sacrifice Amane's peace of mind and happiness, Faris' father and Ruka's chance to live as the gender he identifies with.
Shrouded in Myth: In the future, Okabe is a legendary terrorist, but apparently not much about him is known. This leads to Suzuha taking Okabe's nonsense utterly seriously in the present since she doesn't know that Okabe was actually just some dorky university student in 2010. It all sounds about right to her, after all.
Smarter Than You Look: He seems like an idiot, especially early on, but as the story progresses it turns out he has a really intuitive way of understanding things and finds it easy to explain them in simple terms. In the present, he and Kurisu handle the bulk of the theoretical work while Daru handles tech stuff. In the future, he even invents a full time machine and a device to measure temporal deviations. Maybe his claims about his IQ were true after all.
A Tragedy of Impulsiveness: The opening of the story is a Flash Forward of Okabe cursing himself out for repeatedly acting without thinking with something as dangerous as time travel. He keeps sending D-Mails back even after the first big change caused by Moeka makes him realize that the world can change in massive and unexpected ways from the smallest of actions. After this, he allows the past to be changed three more times, each time vastly altering who is around him and how close he is to ensuring Suzuha's bad future.
Tsundere: He hides behind his eccentricities when he's being nice to people because he's kind of awkward. He's not very subtle about it either. Even his internal monologue refuses to admit that he likes anyone. For example, the only time he notes that Kurisu is attractive is their first meeting when he's baffled as to why she's even talking to him. Also, his heart is beating fast from the sense of danger and no other reason, got that?
What You Are in the Dark: Kurisu suggests that if Mayuri's life is at stake and time travel will revert any damages he causes, he could simply physically force Rukako to tell him her mother's old pager number or kill Moeka to take her phone. He refuses.
Would Hit a Girl: Despite his initial reluctance, when he deems it necessary he attacks Moeka, pins her and nearly kills her in order to take her phone and try to save Mayuri.
Labmem 002 and called Okabe's "Hostage" after a game he made to cheer her up, which is the foundation of his current chuunibyou schtick. Though his childhood friend, she's two years younger and is still in highschool, so he views her as a little sister and works hard to support and protect her. She's noted to be fairly useless as far as advanced physics go, but nobody minds since she makes sure everyone gets along. She works at the maid cafe May Queen with Faris and enjoys trying to make Ruka wear the cosplay outfits she designs herself.
Catch Phrase: She likes to greet everyone with a friendly "Tutturu~"
Childhood Friends: She's been friends with Okabe for a long time and she's actually the one responsible for his Mad Scientist schtick: When she was depressed after the death of her grandmother and seemed to be wasting away, Okabe began to act cartoonishly and treat her as his 'hostage' to make her move on. Later in the story, when forced to choose between the woman he loves and his little sister figure, he undergoes a sort of breakdown and is eventually compelled to save Mayuri anyway.
The Confidant: Mayuri has a hard time keeping up as the story begins to escalate, but she always, unfailingly offers a shoulder the others can lean on.
Cosplay Otaku Girl: She loves cosplay, but is only interested in making the costumes and having others wear them.
The Cutie: She's sweet and innocent in contrast to the other three primary members of the group who tend to be the ones really doing the work on the time machine. Her primary contribution is bananas to experiment on which causes SERN to view her as expendable and mark her for death.
The Ditz: It becomes pretty clear that whatever good qualities she may have, a high intellect is not one of them. She tends not to understand anything that's going on in the lab and unlike Daru doesn't seem to get it even after having it simplified. When Mayuri says that one of the names Kurisu came up for to describe what they're doing was too complicated, Kurisu nearly says it doesn't count because Mayuri is dumb, which Okabe catches her on.
Futile Hand Reach: She sometimes reaches her hand to the sky, a gesture Okabe calls "Stardust Handshake." He's not quite sure why she does it, but it makes him a little uneasy.
Gamer Chick: She's a big fan of RaiNet but there's no indication that she's actually any good at it. Rather, she just thinks the mascot is adorable.
The Heart: She's not good at the whole time travel thing, but she is good at making people get along.
Incorruptible Pure Pureness: She's a pretty mild example: While Okabe and Daru are all gung-ho about hacking into SERN and other dubious activities, Mayuri disapproves even when it's clear that SERN is up to some pretty shady business.
The Ingenue: She's very innocent, right up to the point of repeating whatever dirty sounding things Daru asks her to without comprehension.
Kill the Cutie: The turning point of the story comes when SERN deems her expendable and disposes of her. From that point forward Okabe goes through loop after loop to save her from Moeka, SERN and even the universe itself, which views her as 'dead.'
The Load: Okabe admits early on that Mayuri adds nothing to the lab since all she does is sew clothing for cosplay. She’s around because she’s Okabe’s friend and it doesn’t really matter if she’s useless. Of course, when the plot gets more involved she’s as useless as before, causing her to get worried about Okabe since that’s all she can do.
Locked Out of the Loop: During the later story arcs she notices Okabe is very stressed out, but since she's the one person he's not willing to walk about this problem with under any circumstances, she's left feeling like a burden.
Morality Pet: While Okabe and the rest of the characters aren't really jerks, they're all a bit lacking in social skills. Mayuri tends to bring out the nicer sides of all the characters.
Nice Girl: She's happy, friendly, supportive and social in contrast to the aloof and tsuntsun Kurisu or emotionally bottled Moeka.
Nice Hat: Almost always wears a wide brimmed, frilly looking blue hat.
The Not-Love Interest: Mayuri is Okabe's oldest and dearest friend, and we see how much effort he puts in trying to prevent her death. It eventually comes to a head when Okabe has to decide whether to save Mayuri or his actual Love Interest, Kurisu.
Protectorate: Effectively what Okabe means when he calls her is "hostage".
Smart Ball: She's not very bright, but she does have strong intuition and tends to be more emotionally perceptive than those around her. She's even the one to figure out who Suzuha's father is thanks to actually paying attention to what people say and do more than Okabe or Kurisu would.
Static Character: She starts sweet, slow and a little ditzy and ends sweet, slow and a little ditzy.
Stealth Hi/Bye: If Okabe doesn't keep an eye on her, she'll frequently wander off somewhere without saying a thing the moment he looks away. He calls it her "Sneaking Fadeout".
Labmem 003 and Okabe's best friend. He considers himself a Super Hacker and is an otaku with an unhealthy obsession with moe, but is almost as good at hacking as he claims and manages to access the SERN database. He has a crush of sorts on Faris, but he's not too serious about it. He doesn't get a lot of the advanced physics, but his skill with hacking and electronics more than make up for it.
Big Fun: He's a big, fat and somewhat messy guy, but he helps keep the mood going with his generally laid back personality.
Bromantic Foil: You need quite the contrast to make Okabe look attractive, so Daru is fat, perverted and sometimes obnoxious.
Character Name Alias: His codename is derived from changing Daru to Itaru and then translating the word to Barrel. Barrel Titor.
The Cracker: He's an amazing hacker and is easily able to get into the SERN database, though when he comes up into a special code he's unable to break through it, which forces the group to find a rare old computer that can read it.
Deadpan Snarker: He's rather sarcastic when it comes to Okabe's eccentricities.
Disappeared Dad: In the Alpha timeline, he appears to be somewhat recently deceased, though he wasn't around to raise his daughter much either. It's very important to Suzuha to find him, though she knows little about him apart from an alias he used.
Everyone Has Standards: While he mostly makes sarcastic quips towards Okabe, Kurisu states that even he was worried when he saw Okabe crying.
Future Badass: In the SERN timeline, after Okabe dies in 2025 Daru begins to lead the terrorist group at the expense of raising his daughter and builds a time machine, though it was not fully operational.
Lovable Sex Maniac: Whenever a girl lets loose an Accidental Innuendo, he'll ask them to repeat it. He also insists on having all the technical stuff explained to him in terms of eroge.
Otaku: 2-D girls are the only girls for him! Except when they aren't, of course.
That's What She Said: He tends to irritate Kurisu by interpreting everything she says in a dirty manner.
The Watson: Daru is intelligent enough to keep up with a little prompting, but he’s not really into physics like Kurisu or Okabe, so they have to explain the plot to him in simple terms. With varying degrees of success.
Yuri Fan: Daru never turns down the opportunity to imagine his non-Okabe friends having lesbian makeouts. Even Ruka.
Kurisu is an 18-year-old Teen Genius apparently killed at very beginning of the story, only to appear both alive and confused at Okabe's assertion that she's supposed to be dead. She becomes the fourth and final of the primary lab members and does a lot of the work on the time machine. Despite her excellent skills in physics, she's actually a neuroscientist. More than that, she's also a Closet Geek and noted to be quite the blatant tsundere.
A-Cup Angst: When Mayuri tries consoling the retconned into female Rukako about chest size not mattering, Kurisu does a Spit Take.
Adaptation Dye-Job: Kurisu's hair is brown in the original visual novel, but has red hair in the anime.
Agent Scully: Initially, Kurisu completely denies any possibility that time machines could exist. Her tune quickly changes when she ends up helping Okabe build one.
Amnesiac Lover: In the True Ending, Okabe has saved Mayuri, Kurisu and the future, but in exchange, she doesn't remember him. However, fragments of her memories survive, and she feels compelled to track him down anyway, which is expanded upon in the bonus episode for the anime. In the movie, Kurisu successfully falls in love with Okabe all over again.
Back from the Dead: The first plot point of the series begins when Okabe sees her lying in a pool of blood, calls Daru about it and then ends up in a world where for some reason she's perfectly okay. When he returns to his original world, she's dead, but then her death gets a Cosmic Retcon and she's back again.
Faris: Ah...! But... [my] clothes might not fit on you, nyan. Kurisu: By that... do you mean my breasts? MY BREASTS, RIGHT?! Faris: Your height, nya. Kurisu: You... forget I said that.
Character Name Alias: While Okabe uses his Hououin Kyouma identity on @channel and Amane Suzuha uses John Titor based on wordplay and the name of a third party, Kurisu uses KuriGohan and Kamehameha in the same threads. Smooth.
The Confidant: As things get more and more out of hand, Kurisu becomes one of the few people Okabe can confide to for help. Despite lacking Okabe's memories, she does her best to understand his situation provide whatever aid she can. In the movie, she lampshades how he could never have gotten far without her and the others.
Cordon Bleugh Chef: Kurisu enjoys making salad. Grapefruit salad. With some natto and ground beef thrown into the mix.
Kurisu: Mixing stuff in makes it tasty. Grapefruit's sourness makes it a perfect match for anything.
Okabe: No, it doesn't!
Kurisu: Does too. You should try it.
Okabe: There's a salad right here! One that's already made! And it's 50% off—
Kurisu: —Ready-made stuff's no fun.
Closet Geek: Daru and Okabe recognize her quickly as a @channeler despite her frequent denials. She tries to hide it, but she keeps slipping up and dropping obvious memes into her speech.
Cry Cute: After Okabe yells at her for calling him by his real name, Kurisu acts fairly defiant at the perceived anger. When she realizes he's just being his usually goofy self, she's so relieved after the fright that she tears up a little. Despite her Suspiciously Specific Denial, he seems baffled as to why she's sniffling.
Deuteragonist: Kurisu is absolutely by Okabe's side for every loop whenever he needs her. In the future he's the great terrorist and she's the great scientist. The true route is focused on somehow managing to save both her and Mayuri.
In the movie, she gets promoted to lead.
Friendless Background: Focused exclusively on the sciences at a young age, eschewing just about everything else.
Guilty Pleasure: Posting on 2channel, dropping internet slang, just to name a few. Often becomes embarrassed when Daru and Okarin point them out.
Heroic BSOD: In the movie, an attempt to help a younger Okabe backfires when she trips in the rain and causes him to be killed by a truck. Kurisu makes it back to the Steins Gate timeline unharmed, but her morale and emotions are wrecked.
Historical Hero Upgrade: In universe: In one future timeline she's referred to as the mother of time travel, but this is propaganda. Plus, she was forced into it after SERN raided the lab, killed Mayuri and captured her.
Hypercompetent Sidekick: While Okabe is certainly intelligent enough to keep up, Kurisu's knowledge of physics and grasp of the time machine mechanics are probably Okabe's most valuable assets during each of his time-leaps.
In-Series Nickname: Multiple nicknames used by Okabe, mainly "Christina". There's also "The Zombie" or simply "Assistant". There was also the short lived "Celebrity 17" or "Celeb-17".
Intelligence Equals Isolation: Prior to knowing Okabe & the lab members she doesn't seem to have had any friends. Like her father, her coworkers are jealous of her accomplishments at her young age. In one fairly comical scene between herself, Daru, and Okabe, she unintentionally reveals she's a virgin and has never been on a date.
She rushes back to the lab to announce her feelings to Okabe, but mere seconds prior, he had reversed the first D-mail. She's warped from the room and subsequently killed in the first timeline.
It happens again in the movie. The only difference is that this time Okabe is the one to vanish from the room as he is RetGoned out of the timeline. She's even interrupted in almost the same spot in the sentence.
Omnidisciplinary Scientist: Is a neuroscientist, but is apparently well-versed enough in theoretical physics to conceptualize and build a time machine since she also studied theoretical physics to impress her father.
Parental Neglect: Kurisu's father keeps a distance from her, downright refusing to see her. When they finally speak at the end, it's obvious that he's extremely jealous of her and, in the original timeline, killed her to steal her work.
Perpetual Frowner: Kurisu always has a grumpy frown. The only time she doesn't is when she's smirking at Okabe's expense.
Red Herring Mole: Thanks to her role in the future Suzuha believes her to be SERN's spy, leading viewers to the same suspicion until Moeka reveals her true colors.
Sarcastic Devotee: Frequently exasperated with Okabe's antics and wonders why the rest of the lab even follows him. At the end of the day, she's incredibly loyal and helpful to him.
Sacred First Kiss: Before Okabe undoes the final alteration to the timeline he realizes that Kurisu won't survive it and that he's fallen in love with her. After talking to her about it and explaining everything, she gives him a kiss goodbye, accepting her fate.
Okabe informs Kurisu after the fact that this was not his first kiss.
Ironically, it is Kurisu who gave Okabe his first kiss. In the movie, Kurisu saves Okabe by giving him a kiss in the past. The memories of that kiss overpower his Reading Steiner and prevent him from being erased from the Steins;Gate world line.
Sacrificed Basic Skill for Awesome Training: During school, she focused entirely on mathematics to the exclusion of everything else. The only one that really comes up, though, is that she's not very well socialized.
She Knows Too Much: It's implied that she's executed by SERN after completing their time travel device.
Smug Smiler: After Okabe annoys her with his heckling, she addresses all stupid questions and ideas as though they came from Okabe throughout the lecture. When she sees him surprised by something she said, she smirks. She’s not much for genuine happiness, so this is about it for smiles as far as Okabe is concerned in the future as well.
Star-Crossed Lovers: A relationship with Okabe is next to impossible since in one timeline she dies just after meeting him and in the other they end up on opposing sides of global conflict. The only way for it to work is to find the Steins Gate choice and remove both bad timelines from the equation.
The Scapegoat: In the future, she's known as the mother of time travel. SERN values her for this, but groups that oppose this aren't happy at all. In truth she was a captive forced to research time travel, but because Amane doesn't know this she really hates Kurisu and assumes she's a spy.
Teen Genius: From an early age she studied math and science like crazy at the expense of everything else, which has left her a more respected scientist than her father even though she's seventeen when the story starts.
Took a Level in Badass: She's one of the 2 guest characters in the 2D fighting game Phantom Breaker, and is the only normal human but she can fight an even match against superpowered adversaries using lab gadgets. It should be noted that she's among the only 2 characters who have 2 supers.
Trust Password: The first time she gets Okabe to open up about time travel, she tells him that it'll be easy to get her to believe it again when he goes back in time. Turns out she doesn't! Luckily, she told him what she was looking for most at the moment was My Fork, something that both highly embarrasses her and finally convinces her.
Tsundere: She's a highly stereotypical tsundere despite her protests and despite the cast that she really ought to know exactly what characteristics to avoid. She tends to be grumpy and sour to Okabe, but she's also always there to help.
Unwitting Instigator of Doom: Her expertise in physics can be co-opted since she's just a young, relatively unknown student. In the timeline the story primarily takes place in, she was captured by SERN and forced to perfect their time travel and died not long after. In the other time line, she was murdered by her father and her research was stolen and taken to Russia. This sparked a nuclear war that killed five and a half billion people.
You Have Outlived Your Usefulness: In the bad future, she's captured by SERN and forced to assist them with time travel research, with finishes in 2034. Super coincidentally, she dies immediately afterward. To paraphrase John Titor, there are two kinds of people in SERN's dystopia: Those who live extremely long lives and those who die suddenly under mysterious circumstances.
Moeka is a silent and inexpressive young woman who prefers to communicate through her cellphone. She's looking for the IBN 5100 and is the fifth person to join the lab after Okabe bumps into her taking photos for the newspaper she works at. If left to her own devices, she'll never speak, but will send dozens of gigantic text messages at a time until the receiver is forced to respond. She doesn't contribute to the time travel work, but she sends the first major timeline altering message to the past after she says she regrets her choice in cell phones and wants to redo it.
Adorkable: She's too socially awkward to talk, but during the third chapter she sends boatloads of mails that show that she's too scared of the dark to come knock on the door of the lab and other numerous goofy emails. Which makes quite the contrast when she coldly and professionally kills Mayuri despite a previous mail indicating she found her hilarious. During Moeka's arc near the end a middle ground is found between these two poles in that her awkwardness, while cute, has also made her a weak, dependent and easily manipulated doormat, explaining the contrasting attitudes.
Driven to Suicide: When she stops receiving FB's messages in the last loop due to having outlived her uselessness, she eventually commits.
Emotionless Girl: Moeka never shows any expression on her face or in her voice unless you do something like try to take her phone, though by reading the mail she sends it's clear how she feels about everything.
Extreme Doormat: She tends to be extremely passive and willing to follow directions from FB even if they're orders that she's clearly not happy about carrying out such as killing her friend Mayuri. She doesn't even hesitate.
Jumped at the Call: Right after a failed suicide attempt, she was contacted to join the Rounders. It gave her life meaning to be in contact with someone that would listen to her like FB.
Meganekko: Her glasses help her look withdrawn and timid.
The Glasses Come Off: She's missing her glasses when she reveals to the lab members that she's a SERN agent.
Knight of Cerebus: After FB gives her the word, Moeka will not rest until she has Mayuri dead and the rest captured.
The Mole: She joins the lab group largely because she's also looking for the IBN 5100 and once she has everything she needs, she leads a team to capture them all apart from Mayuri, who is marked for death instead.
Perpetual Frowner: Her life is pretty empty, so she always looks essentially expressionless and depressed. When in the lab for the first time she seems intrigued by these people, but since she looks so emotionless it's a little hard to tell.
The Quiet One: She hates having to speak, but when using mail she's a real chatterbox to the point where the frequency of her messages really irritates Okabe. She begins talking just a bit more frequently by the time the movie comes around.
Shrinking Violet: She's too shy to talk to people directly and tends to be reclusive, which rather jars with her job as a journalist. At one point she threatens that she knows Okabe is in the lab and is going to come knock until he comes out, but when she actually gets there (Okabe slept through these messages) she gets too nervous to actually try it since the building is too dark. On a less cute/comical note, her poor ability to interact with others left her feeling isolated and miserable, which made it easy to recruit her into the Rounders and follow any order her superior gave her.
Stalker Without A Crush: She's almost silent in person, but with a phone in her hands she'll obsessively send gigantic text messages over and over no matter how irritated her subject gets at the attention. While Okabe is the one to get most obviously annoyed and wish that she would quit it, she's actually even worse in relation to her boss, who has gotten quite sick of it but has to keep responding anyway.
Subordinate Excuse: She's a Rounder not because she cares about SERN or time travel, but simply so that she can continue to talk to her surrogate mother FB.
Undying Loyalty: She places complete faith in her supervisor, FB. She'd do anything for her, though she's too afraid to meet in person or call directly.
Ruka is Mayuri's classmate, an extremely feminine looking boy who works at his family's shrine. He seems to worship Okabe, who believes they have a master/disciple relationship. He's very shy and soft spoken and before the story began was too nervous to ask to join the group, so he becomes the sixth member to join after Moeka and Kurisu have already joined. Like Moeka, he's allowed to send a message back to the past because he hopes he can use time travel to make himself be born as a girl. Somehow.
A-Cup Angst: He retroactively becomes a girl (don't question it!) but looks identical. Meaning completely flat chest, something she's not proud of.
Instant Web Hit: According to the Visual Novel, pictures of Ruka in cosplay got leaked on the internet while Okabe was in the hospital for his stab wound, and he's now regarded as one of the internet's most popular "Traps".
Let Them Die Happy: In Ruka's ending she gets to be the only person not named Okabe to use the time leap and make sure to use it to have Mayuri's last day be a happy one rather than what would normally have happened.
Miko: Despite being male, Ruka seems to work as the shrine miko anyway, which doesn't help when it comes to being recognized as male.
Shrinking Violet: He's very shy and quiet, so Okabe seems to have taken it upon himself to give him manliness lessons by practice swinging a fake sword.
Single-Target Sexuality: When a female, Ruka recounts their first meeting to Okabe and confesses that it was Love at First Sight. However, what she is remembering is how they first met when Ruka was a guy, but in miko attire, and Okabe was completely unconcerned and accepting of that. Okabe realizes that Ruka's feeling are probably still the same when she's turned back to normal, but is unable to answer them.
Transsexual: Ruka wishes he had been born female, though it's not clear if it's because he's genuinely transsexual or because he knows Okabe will never fall in love with another man. A D-mail is sent to somehow turn him female. To save Mayuri, Okabe eventually has to crush Ruka's happiness and return her to normal.
Unsettling Gender-Reveal: Everybody who sees Ruka assumes he's a girl. Kurisu is particularly shocked to learn the truth. When Ruka is retroactively turned into a girl, the one in for a surprise is Okabe, who has grown used to thinking of Ruka as a guy and tries to grope her to prove it. Doesn't work out as intended.
Wholesome Crossdresser: He's seen wearing a shrine maiden outfit fairly often. Mayuri wants to make him wear female cosplay clothing as well.
Yamato Nadeshiko: Ruka is very feminine, supporting and domestic, but... he's a guy!
Faris is Mayuri's coworker at the May Queen Cafe as well as the owner. She's able to keep up with Okabe's fantasies because she seems to be living in one of her own. She always wears a pair of cat ears and does the typical 'nya' verbal tic even off duty. Likes to play with Okabe, but he finds her kind of annoying since she's better at making up weird melodramatic stories. She's secretly quite wealthy and becomes the seventh member to join the lab group. She keeps the content of her mail a secret
Cat Smile: Her default expression is a playful smile.
Cloud Cuckoolander: She has an irritating tendency (to Okabe, at least) of being able to play right along with his delusions since she's every bit the space case that he is. It leads him to feel that he cannot beat her.
Cosplay Otaku Girl: She loves dressing up as a cat eared meido despite being rather wealthy. The ears in particular almost never come off.
Crocodile Tears: When Okabe is understandably doubtful about her honesty regarding the need to use time travel to win a Rainet match to improve her memory, she makes him go along with her by pretending to cry.
The Cutie: She has an extremely cutesy attitude. It's something of a stage persona at times, but mostly just something she enjoys doing.
Disappeared Dad: Her father died when she was little, but he's alive in the timelines after she sent her D-mail.
I Lied: After successfully using a D-mail to go back and win a tournament, Okabe asks her to fulfill her end of the bargain and tell him how to undo her D-mail, after which she admits that her future self had probably just lied since she wanted to win really badly. And then she ends up remembering for real and really crying.
Improbable Age: Believe it or not, 17-year-old Faris owns Akihabara, and is responsible for making Akihabara into moe town. In the altered timeline with her father still alive, she didn't have the influence or desire to make it into a moe town, so there's no anime stuff anywhere to be found.
Large Ham: In similar fashion as Okabe's Hououin Kyouma persona, Faris enjoys her theatrics.
Living Lie Detector: By looking at people, she can tell how honest they're being to a rather precise level.
Love Confession: If you skip the D mail that gets you into chapter 8, you end up at the Faris ending where she confesses before Okabe even sends back the mail. He tries to ignore her confession. In a rare moment of honesty, she sighs and admits it's a bit tiresome that he always evades her like this.
Mega Twintails: She has massive pink twintails since she likes to dress like an anime character.
Ms Imagination: Like Okabe, she seems to love holding onto delusions. For her, she styles herself as the great Faris Nyannyan, a cat girl meido. Much to Okabe's irritation, she's better at it than he is: she's pretty quick witted and can just absorb all of his posturing into her own scenario.
My Greatest Failure: The last time she saw her dad, she got in a fight with him. She hasn't been able to live it down.
The Ojou: She's extremely wealthy and has quite the wealthy lifestyle, though she keeps this hidden from most people.
Parting Words Regret: The last thing she said to her father before he took off for a business trip instead of spending time with her was her yelling that she hated him.
Rose-Haired Sweetie: Her energetic, playful attitude and pink hair matching is quite possibly not a coincidence at all: As much as she loves anime culture and considering the otherwise natural-ish hair colors, it could be dyed.
Amane is a teenaged girl who works at Mr. Braun's shop. She likes to ride her bicycle and gets along very well with his daughter Nae. She's very physically fit and a friendly person, but her rather strange vocabulary can be difficult to deal with. She has an instant antipathy towards Kurisu, but is still the eighth and final member to join the lab. She doesn't send a message to the past, but Okabe sends one on her behalf
Action Girl: She's very physically fit and calls herself a warrior, which Okabe refines to Working Warrior. When Moeka attacks on the 13th, Suzuha is the only reason they make it out okay when she charges in and attacks the SERN operatives all by herself.
Back for the Finale: She largely exits the plot when she goes back in time to get the IBN 5100, but returns at the end as a different alternate future self than the one Okabe knows and is here to prevent World War III.
Driven to Suicide: In one timeline, her older self committed suicide after having failed to complete her mission. In others, she passes away due to illness.
Exact Eavesdropping: Thanks to the windows being left open and Okabe's excessive volume Suzuha overhears a lot of what they're working on. Though you could also read her hesitation before giving this answer as her just making an excuse. After all, she doesn't have to overhear anything, she already knows that Okabe becomes a terrorist opposing SERN.
Extreme Omnivore: She mails Okabe to ask if there’s anywhere to find bugs or weeds to eat.
Improbable Age: She's only eighteen, but considers herself a warrior and is a veteran terrorist used to fighting SERN. She even alludes to having been captured and tortured once.
A CRT-TV store owner, and Okabe's landlord. Though a large, imposing man, Yuugo is a doting father towards Nae and wishes to shield her from Okabe's... eccentric activities. He is referred to as Mr. Braun due to his love of braun tubes. Though gruff, he rather likes Okabe.
Bald of Awesome: With his physique and shaved head, he's definitely designed to have a manly look.
Bruiser with a Soft Center: He's big, irritable and threatens Okabe frequently, but he cherishes his daughter and actually likes Okabe.
Covert Pervert: When Suzuha distracts him with her 'seduction' technique by taking off her jacket and attacking his face with it, Okabe turns on the 42 inch TV so the lab can use the Microwave Ophone. When he reenters a moment later, he expects to be punished severely... but Mr. Braun thought it was pretty kinky and doesn't mind at all.
Cranky Landlord: With Okabe for a tenant, it's forgivable, but he tends to threaten to hit Okabe or raise his rent frequently.
Dark and Troubled Past: In his youth, he was homeless and lived a miserable life, though a kind and reclusive woman name Suzu helped him out and earned his complete and unshakable gratitude. When SERN offered him a job as a hitman "Rounder," it turned his life around, but came at the cost of his freedom.
Disco Dan: He's a huge fan of CRTs even when HDTVs are commonplace at this point.
Overprotective Dad: Braun forbids Okabe from talking to, being alone with, or standing in close proximity to his daughter, either to keep her away from his experiments or... other reasons.
Silent Scapegoat: In Mayuri and Kurisu's ending he vilifies himself in front of Moeka to drive her away from him and takes credit (an act that will get him killed by SERN) in order to keep her safe. It doesn't work, though, because either she commits suicide when cut off from him or because a time displaced Nae murders her. When the world wants you dead, it'll jump through whatever hoops it has to.
Yuugo's daughter who is good friends with Mayuri. She appears to be slightly afraid of both Okabe and Daru, but gets along well with everyone else.
Cheerful Child: Nae represents raw innocence, the most important part of humanity. Something to be protected.
Children Are Innocent: She's very sweet and friendly, though shy around Okabe due to his loud behavior. However, in an alternate timeline, her father commits suicide and Nae swears bloody vengeance against Okabe. She then time jumps back inch by inch and sends herself even crazier before ending up back in her child's body.
The Cutie: It is through their interactions with playful, sweet, innocent Nae that many of the characters reveal their soft sides.
Demoted to Extra: She briefly plays a fairly large supporting role near the end, but this is excluded from the anime.
Living Emotional Crutch: Mr. Braun has stated several times she is everything to him. It is implied he would have committed suicide long ago if not for his daughter.
Morality Pet: She keeps her father's anger in check anytime Okabe gets on his nerves. On the other hand, to protect her, he became SERN's subordinate.
A mysterious poster who appeared on @chan. While he says the same things as the John Titor in the real world, nobody remembers the first appearance of Titor and he claims himself that he has not been to the year 2000, though he may go in the future. He's an early source for information, though Okabe is understandably leery about trusting him.
Character Name Alias: Named is based off a revolutionary/terrorist hero from the future, though Titor himself doesn't realize where the name comes from.
Fish Out of Temporal Water: Titor doesn't really get internet lingo, nor a lot of informal speech. He even fails to realize when people are making fun of him. Titor's true identity, Amane Suzuha, acts similar in real life. She takes Okabe's Kyouma persona at face value, refers to herself as a warrior and occasionally drifts into some rather odd word choices that take Okabe a few moments to puzzle out. [[spoiler:She's from a future where she constantly fights and only knows Okabe as a deceased revolutionary leader who helped invent time travel devices, so from her perspective everything he says sounds about right, if perhaps a little dramatic.
You Have to Believe Me: Averted. Though worried about the future dystopia brought on by SERN, he says he doesn't really care if anyone believes him or not. He never gets excited or overly defensive, leaving his excitement at finding someone who remembers alternate timelines his only real emotional reaction.
FB is the operative in charge of SERN's rounders in the area. FB is assumed to be female, but nothing definite is known until near the end of the story.
Adaptational Villainy: Unlike in the visual novel, in the anime he doesn't try to protect Moeka from the fallout. He kills her himself before committing suicide.
Living Emotional Crutch: Moeka is completely dependent on FB, who functions as a surrogate mother figure for a woman who who was on the verge of suicide due to her isolation.
The Man Behind the Man: FB is Moeka's supervisor, though the two haven't met face to face since such things are discouraged. This is the closest we get to the true face of SERN.
Manipulative Bastard: FB controls at least some subordinates by reaching out to them at their lowest moments and recruiting them into SERN, leaving them almost fanatically loyal. However, he actually does care about Moeka even if he finds her annoying.
Punch Clock Villain: FB takes time to console neurotic employees, no matter how annoying they may be. The villainy isn't really by choice, either, but is simply done so that he can actually provide for his daughter. He didn't want to actually find the computer SERN was looking for.
Doctor Nakabachi is a crackpot physicist obsessed with time travel. He is not taken seriously in the scientific community. The story begins with Okabe attending his conference simply to make fun of him for attempting to publish internet conspiracy theories about time travel as though they were true.
Broken Pedestal: He's idolized by his daughter Kurisu who wants to get close to him, but when we see them finally speaking at the end he's a complete ass, blames her for his own failings and loudly announces his intention to steal her work. He's even willing to kill her when she realizes what he's like.
Green-Eyed Monster: His envy of his daughter, Kurisu has severely unbalanced him to the point where he attempted to kill her in the original world.
Jerkass: He's a complete asshole, making it easy to ignore him.
Laser-Guided Karma: In the True Ending it seems as though he'll get away with trying to murder his daughter to steal her research but then we get a little update: A plane fire destroyed the stolen research and he began ranting and raving, discrediting him further. What's more, he's under suspicion for stabbing Okabe.
Miles Gloriosus: He loudly proclaims himself as an amazing scientist when he's actually quite incompetent and no stranger to stealing the work of others, which Okabe calls him out on at the start when he stole research from an image board.
Nom de Mom: Inverted, his real name is Shouichi Makise, but he changed his name due to his issues with Kurisu.
Plagiarism In Fiction: Steals the work of John Titor and begins his research with it. Also turns out that in the original world he attempted to kill Kurisu after she said in shock that he planned to steal her much better time travel research and publish it solely under his own name.