Though Taichi doesn't speak much, he's very sympathetic towards others and wants to help his friends when they're having trouble. He tends to become very passionate and gets carried away whenever he starts talking about his hobby, pro-wrestling, and Inaba stops him when he tries to add wrestling topics to their Student Cultural Society's newspaper. He has a little sister in elementary school, Rina.In the story he is the prime example of Chronic Hero Syndrome and Martyr Without a Cause. This trait of his is explored both as his greatest strength and weakness as the series progresses.
Eventually, by the time of Heartseed's 6th phenomenon, his underlying Martyr Without a Cause problem is brought to light, and the arc highlights how Taichi lacked a mind of his own, that he merely blindly responded to the wishes of others and never stop to think about his own perspective, approach or responsibility to the situation, or whether it was in the best interest of the others. In both Inaba and Fujishima's words: He is like a mindless, RPG game avatar. This eventually led to him causing trouble in the school and injury for his classmates, as well as Inaba breaking up with him, who was deeply pained by his seemingly lack of concern regarding their relationship. It was a harsh lesson for him.
Laser-Guided Amnesia: He loses his memories of the Cultural Club and everyone in it due to the Forced Termination phenomenon in Nise Random. He manages to recover thanks to Chihiro and Shino's efforts.
Loss of Identity: By Yume Random it is full blown. Taichi has become so wrapped up in playing the hero he has completely lost sight of himself.
My God, What Have I Done?: Due to his personality, he has done quite a number of things that he regrets right away throughout the series. Such actions include hurting Iori and allowing his selfless obsessions to get between him and Inaba.
Taking the Bullet: Takes a lead pipe to the head while protecting Inaba from a thug. He recovers.
Tempting Fate: When Iori first open up her identity problem to him, he promised that "No matter what happens, no matter what you've become, I will know that Nagase is Nagase." Well... guess what happens next episode...
Iori is Taichi's classmate, a bright, friendly, popular girl. She's the president of the Student Cultural Society, but rather than lead everyone, she sets the mood and gets them excited. Occasionally she takes bold actions in front of others, be it due to carelessness or simple naivety.She had 5 different fathers in the past. And as her first stepfather turned out to have violent tendencies, she had learned to alter her personality to appease and fit the expectations of others to the point where she had become unsure who she was originally supposed to be.
Abusive Parents: Her first stepfather turned out to be like this and he became the reason why Iori started taking on multiple personalities.
Beneath the Mask: As revealed in Michi Random, her true self is moody, critical and angry. It is later revealed that this was just another extreme persona Iori conjured up, hoping it was her true self. Eventually, Iori decides to just stop caring and act however she likes. The true Iori is something in between the extremes, bubbly and loving, but also firm when she needs to be.
Everything but the Guy: Iori ultimately decides against dating Taichi. By the end of the series, she remains single, but has grown significantly as a person, rescued her mother from a terrible decision, amassed a group of loving friends, and conquered her Loss of Identity. She does admit she wouldn't mind getting a boyfriend eventually though...
The Social Expert: A factor of her persona changing. Iori has become accustomed to reading and anticipating the social cues of others, allowing her to predict their motives and true feelings, which she can then adapt to.
Split Personality: Not a case of actual different personalities, but more on the lines of her wearing multiple masks, while not having a mirror to see her own face.
The Tease: She loves making perverted jokes around Taichi.
Himeko is vice president of the Student Cultural Society. She excels in gathering information and analysis, possessing private data on each of the club members. She's calm and logical, but she's also rather blunt, so she has difficulty dealing with delicate situations.Due to certain reasons she prefers everyone else, with the exception of her family, to addressed her by last name, Inaba. She had an inherent difficulty in trusting anyone including herself. However, as she had pointed out herself, unlike her friends she did not experience any particular trauma; she was born with such personality. She deeply despises herself for this, which results in her rather negative self-esteem.
Clingy Jealous Girl: After Iori innocently hugs Taichi and calls him "onii-chan" (big brother), Inaba looks visibly irked. As Iori continues to innocently say things, Inaba continues to get a bit angry at him for apparently enjoying it. She is full-blown once she starts dating Taichi.
Corporal Punishment: She seems to regularly administer forehead flicks when a club member steps out of line.
Covert Pervert: Surprisingly she can be quite perverted, every volume she says at least one sex-related phrase or topic (Which are of course all directed towards Taichi). The fact that she is dead serious about what she says sometimes, doesn't help.
Inaba: "Ah... Is that so... Taichi thinks I smell good... Then again I'd really want a chance to blend our scent together soon." *giggles*
Genre Savvy: Catches onto how Heartseed thinks fairly quickly.
First Kiss: Was technically taken by Taichi twice. The first time was actually Nagase kissing Taichi in Inaba's body, the second time was of Inaba's own free will after her Love Confession.
Foil: To Iori. Inaba being the cool, commanding and blunt member to contrast Iori's bubbly, happy-go-lucky and sweet character. The contrast takes on a new meaning when it is revealed both have their own deep-rooted insecurities, and their respective personalities were fabricated to help them cope.
Freudian Excuse: Notably Averted. Inaba actually doesn't know what caused her to become so untrusting and cold. She thinks she was just born that way.
Limited Social Circle: Her social circle does not extend past the Student Cultural Society. Inaba later socializes more, but no relationships are ever as deep as the ones she forms in the club.
Lonely Rich Kid: Well-off family? Check. Crippling chronic loneliness. Check. While it's never outright stated that the two facts are related, the connection between them is utilized to great effect: Inaba's bedroom is positively massive, but almost entirely empty, and almost entirely dark, other than the corner with the computer in it where she's implied to spend most of her free time. The solitude and misery are almost tangible.
Towards Taichi for his "selfless freak" personality in episode 5.
Delivers a rather nasty one towards Yui during her "unleash" in episode 7.
Delivers yet another one towards Iori in episode 16.
And finally, delivers her best ones towards Taichi, again, in Yume Random arc.
Sacred First Kiss: She does not take it well when she hears from Iori that the latter shared her first kiss with Taichi in the former's body. To fuel the Ship Tease, technically both girls had shared their First Kiss with Taichi.
Team Mom: Inaba takes it upon herself to understand and counsel her friends.
Tempting Fate: While making their way to Iori's house, Aoki suggests it would be quicker to take a bus but Inaba states they can't risk anyone seeing them if one of them randomly reverts to a child. Seconds later, Aoki reverts to a child.
Yui is very active and expressive. She's a bit small, but she holds ranks in Karate, and even won tournaments when she was in middle school. She absolutely loves cute things, and her room at home is filled with fancy items. She always ends up insulting Aoki when he tries to approach her. It was revealed that Yui was a victim of attempted rape in middle school, which resulted in her androphobia.
Action Girl: Puts her Karate skills to good use when she, Taichi, and Aoki rescue Inaba in Episode 17.
Laser-Guided Amnesia: She loses her memories of the Cultural Club and everyone in it due to the Forced Termination phenomenon in Nise Random. She manages to recover thanks to Chihiro and Shino's efforts.
Yoshifumi is Yui's classmate. He holds affection for her, and continues his attempts to approach her, but she never gives him a chance. In the Cultural Research Club he's often called out, and his pathetic side stands out more, but he also relaxes them with some of his casual statements.
Abhorrent Admirer: For Yui. It's later subverted, since she doesn't dislike the idea of them becoming a couple, but her androphobia makes it very hard for her to accept his feelings.
Plucky Comic Relief: A Deconstruction of one. Jokes and silly antics are all Aoki has going for him, so he deliberately acts the fool to lighten the mood. Should he ever fail at this role, Aoki will become depressed since that would make him completely useless.
Fujishima is Class 1-3's representative and as such, is a classmate of Taichi, Inaba, and Iori — the latter of whom she is madly in love with. After learning of Taichi's feelings for Iori, she becomes a sort of love rival to him.
Break the Haughty: Downplayed, but Fujishima does not take it well when Setouchi is chosen as class representative instead of her during their second year. This becomes a turning point in Fujishima's character where she becomes more humble and her Large Ham qualities are mellowed.
Friendly Enemy: To Taichi at first, but gradually turns into a straight, albeit awkward, friendship.
The Heart: Throughout the series, whenever the heroes are in a rough patch they can't seem to resolve, she comes out to dispense advice or otherwise lend a hand. She does this for everyone in her class, as just after giving Taichi advice in episode 8, she answers a call from someone else about love problems.
Hero of Another Story: The only supporting character who has a full length side story dedicated to her in the novel.
Homeroom teacher of our unlucky group. Also serves as a host for Heartseed, who occasionally takes control of Gotou's body to explain something to our protagonists. Gotou in his place have no recollection of what happenes at those times. When he isn't spending his time possessed he is a very laid back and friendly teacher; gets by with having his students do his work for him. When he's actually serious he can give out surprisingly good advice, and seem like an actual teacher. However, any time when our protagonists are about to appreciate his wisdom, he reverts back to his usual goofiness (much to their chagrin.)
Butt Monkey: Out of all his students, only Taichi gives him a shred of respect.
Love Freak: Manufactures an elaborate triple date for her friends in Step Time just because she was dissatisfied with the intimacy between the couples. Taichi notes how she's starting to rival Fujishima.
A student of class 1-C. She is known for hanging out with delinquents from other classes. Has a crush on Shiroyama Shouto. She did not take it well when Iori rejected the latter and began bullying her with her delinquent friends. She has gone as far as hiring delinquents from other school to sabotage the CRC's presentation. She regrets it though.
Jerk Ass Facade: Thought acting tough would make her crush notice her more.
Karma Houdini: Lampshaded, everyone is shocked by how easily Iori forgives her, even Setouchi herself.
She even wins the guy she likes later in the novel. Justified in that she did her best to earn him.
My God, What Have I Done?: After she finds out that her little revenge tactic went a bit too far. She hated Iori because the latter turned down a boy the former liked rather harshly, and acted very nonchalant about the whole deal. Then she gets a bunch of guys to ruin the CRC's club room, destroying it along with the work they had done for a presentation. And did not approve of the guys kidnapping Inaba to prevent her from identifying them after they were discovered to be the culprits.
Socially-Awkward Hero: One of the focuses in Step Time is Mariko's awkwardness with dating, having never been on one before despite her usually outgoing personality.
A mysterious entity and the primary culprit behind the many paranormal phenomena that has been happening to the Cultural Research Club members. He communicates with the club members by possessing and speaking through Gotou Ryuuzen, their homeroom teacher and club advisor. His motives and objectives are unknown except for that he thinks the club members are "interesting" and wants to observe them.
Sadist: Deliberately trying to make a group of friends turn on each just to see what would happen lands him pretty close to being one.
Sadistic Choice: In episode 5, Heartseed gives the group the choice of which of their souls will die with Iori's body.
Stealth Hi/Bye: He always seems to pop up wherever and whenever he wants in order to talk with the CRC members. It usually freaks them out when he appears.
Super Reflexes: Heartseed bestows super human abilities to any body he possesses, allowing even the unimposing Gotou to effortlessly block karate expert Yui's attacks.
Super Strength: Strength in general is also boosted well beyond what any average human could be capable of.
Troll: Taken to the logical extreme for someone who has supernatural powers. The struggling and anxiety of the Cultural Club amuses him.
The Voice: Heartseed never appears in person, and that's assuming he even has a physical form.
Another "Heartseed" who debuts in episode 11, serving as the culprit behind the "Time Regression" phenomenon. It claims to be similar to yet independent of the Heartseed that the Cultural Club knows of. To keep things simple, it chooses to refer to itself as Number Two, as in the second Heartseed. Its motives seem to stem from its fascination of Heartseed's relationship with the club members.Also worth noting that, unlike the first Heartseed, Number Two doesn't mind being malicious the slightest. It shows up again in Yume Random, to observe Heartseed. Heartseed is not pleased. And later, in the final arc as well.
A Form You Are Comfortable With: Just like Heartseed. In the novel, Number Two first appears to Taichi through Ozawa Misaki, one of his classmate, then primary through Taichi's sister Rina for the rest of the arc. In the anime, Number Two appears through Rina right away. Taichi is noticeably distressed.
Ambiguous Gender: Whether or not the Heartseeds even have a gender is itself debatable, but Number Two does tend to use feminine pronouns when addressing itself and has strictly possessed female characters only.
Taichi's 10 year-old sister. To Taichi's bewilderment, she's quite knowledgable of love and relationships for someone of her age.
Adorably Precocious Child: She likes to complain about how busy she is with her elementary school club activities and acts superior to her older brother, as if she is taking care of him.
Big Brother Attraction: Invoked during episode 14, when she gives Taichi a "true love" chocolate during Valentine's Day. In episode 15, he has a talk with her about how Brother-Sister Incest is wrong, causing her to laugh and clarify that she was only joking about the "true love" part. She then kisses him on the cheek and Taichi gets reallyhappy.
Hypocritical Humor: She hates how the Cultural Club is always demanding Taichi's attention and threatens to call the cops on her brother for acting like a lolicon. Ok, you got all that? Go read the above tropes.
Locked Out of the Loop: Painstakingly so because Taichi dedicates so much time to his sister. It's a challenge for him to keep such a clever kid in the dark about what's really going on. She learns the truth in Asu Random II.
Guess Who I'm Dating?: Reika decides to get back together with her previously abusive 2nd husband, the one that ruined Iori's childhood and forced her to start faking personalities, which is now preventing Iori from speaking up to her mother.
A new addition to the Student Cultural Society after the main cast entered their second year of high school. He is a fellow karate student whom Yui met in the dojo. When he entered Yamaboshi High, Yui convinced him to join the club.He became the interest of Heartseed in Nise Random, whom gave him the power to disguise himself as someone that the casts know, and requested him to do something "interesting".
A new addition to the Student Cultural Society after the main cast entered their second year of high school. She decided to join the club because she is in love with Taichi's voice.She became the interest of Heartseed in Nise Random, whom offered her the power to disguise herself as someone that the casts know, and requested her to do something "interesting". She rejected it at first, but eventually accepted it when things gone wrong and used the power to help.
A student of class 1-C. She is a member of the track team and has a very spirited personality. In one of the short stories in Clip Time, she makes a love confession to Yui and Yui decides to gives her a chance, though she ultimately decides to just be friends.
Violence is the Only Option: After seeing how those who suffer violence are removed from the Isolation Dimension, Katori comes up with the idea that violence really is the only option, and peace advocating individuals like the StuCS better stay out of the way.
Well-Intentioned Extremist: He's really just trying to help the students escape the isolated dimension and freaky phenomena, however his methods are somewhat... questionable.
Debut in the final arc of the novel as the final antagonist(s) of the series. The culprit(s) behind dragging every first and second year students (except the main cast) of Yamaboshi High into their large scale experiment. Not exactly a single entity but rather how the main cast decided to call the unknown number of Heartseed(s) that took part in the phenomenon after they learn of their presence.
An Even More Deliberately Bad Example: As if Number Two wasn't already bad enough, Number Three(s) dragged pretty much two thirds of the school into an isolated dimension so they could "better experience the amusement."