The game begins with a mysterious young man stumbling onto the grounds of Ashford Academy and encountering members of the Student Council before collapsing. After being asleep for several days, he awakens and is met by the entire Student Council (Student Council President Milly, The Stoic Lelouch, Genki Girl Shirley, Nice Guy Suzaku, Plucky Comic Relief Rivalz, Shrinking Violets Nina and Kallen and Lelouch's younger sister the handicapped Nunnally.
Lelouch immediately demands to know who the young man is, at which point Milly scolds him for asking for someone's name before giving his own. After introductions, Lelouch again demands the young man's name, at which point the youth reveals he is suffering from memory loss. He can just barely remember his name ('Rai' by default).
Lelouch recommends calling the authorities, but Milly decides to accept Rai into Ashford Academy as a new student, allowing him to stay in the school clubhouse to boot. Lelouch is shocked at this, but Milly says she'd feel bad about just dumping someone who's so dazed and confused. Most of the Student Council backs Milly and Lelouch reluctantly backs down, knowing how stubborn Milly can be. Rai himself attempts to refuse, not wanting to be a burden, but Milly insists. Rai tries to press the issue, and in return Milly says he can pay her back by helping with the Student Council.
Thus begins Rai's life at Ashford Academy. The two versions of the game are almost identical, sharing the same four routes (the Geass Route, Brittanian Army Route, Order of the Black Knights Route and Ashford Academy Route) but also having one unique route each (the Japanese Liberation Front Route for the PSP and Blue Moon Route for the PS2). Which route Rai follows depends on which characters he interacts with the most, along with decisions he might make. For example, interacting a lot with Suzaku during the prologue eventually has Suzaku invite him to meet with the Experimental Unit, which can lead to Rai joining the Brittanian Army. On the other hand, spending time with Kallen has her decide to recruit Rai into the Order of the Black Knights.
There are also several routes available within the chosen route. For example, the Brittanian Army route can have Rai remain part of the Experimental Unit, join the Purebloods Unit led by Jeremiah Grottwield and Villetta Nu or even join Princess Cornelia's Royal Guards. For the PSP version Rai can opt to break ranks with the Black Knights and defect to the Japanese Liberation Front. The PS2 exclusive Blue Moon route can have Rai become closer to and eventually romance various characters like Nunnally, Kaguya, even Lelouch himself.
This visual novel provides examples of:
- Bishōnen: Rai and a few of the guys fit this trope well.
- Bi the Way: Rai can romance anyone, regardless of gender or canon sexual preference.
- Break His Heart to Save Him: If the player chooses to pursue Lelouch as a love interest, it's possible for this to happen to Rai should he learn too much without earning Lelouch's complete trust.
- Does This Remind You of Anything?: The "Blue Moon" endings are in a church with Rai and his chosen love-interest.
- The Lelouch version even includes the two of them making vows "under god" to stay together forever and love each other.
- Another example is the PSP-only Japanese Liberation Front Route, where Rai defects from the Black Knights. His interactions with Kallen afterwards resemble a couple going through a rough patch in the relationship and are going through a trial separation, and yet would dearly love to get back together. Nunnally lampshades this during a conversation.
- Multiple Endings: The game features four routes to go down based on choices in the first few days. The Geass Route largely follows the original story, while the Routes for the Black Knights, the Brittanian Army, and Ashford Academy offer different perspectives and courses of events. Each route also has multiple endings based on Relationship Values with major characters in that route.
- Furthermore, the PSP version and PS2 version have routes unique to them (the Japanese Liberation Front route and the Blue Moon route respectively).
- Purple Prose: Rai can be this way at times.
Examples common to all routes:
- Amazon Chaser: Considering most of the girls in the series are badasses in their own right (Cornelia being a Warrior Princess, Kallen being an Ace Pilot, Chiba and Villetta are veteran soldiers), Rai easily comes off as this.
- Bittersweet Ending: Most of the endings fall under this.
- Under the Geass Route, Rai puts himself back to sleep shortly after compelling everyone to forget him. C.C. (who is immune to the Geass) sadly hopes for a day when he can awake and no longer have to fear losing control, the Student Council wonder who'd been helping them and Nunnally feels a deep sense of loss but can't understand why she's so sad.
- Under the Brittanian Army Route (Royal Guard ending), Rai nearly loses control of his Geass and tries Suicide by Cop. It fails and he's brought away by a sympathetic Nonette, but he effectively abandons his rank, his comrades and his princess. Cornelia believes he'll someday return, so it isn't completely hopeless.
- Under the Japanese Liberation Front Route (Kaguya ending), Rai is left comatose after pushing his Geass into overdrive. Kaguya holds out hope he'll wake up someday and resolves to stay by his side til then.
- Under the Ashford Academy routes, Rai successfully protects everyone from terrorists by using his Geass, but once his power is outed he opts to mindwipe everyone and go on the run. His classmates are left wondering if the terrorists took him away.
- But Not Too Foreign: Rai turns out to be half-Brittanian and half-Japanese. It also turns out that his Brittanian half is descended from the Brittanian Royal Family (making him distantly related to Lelouch, Nunnally, Euphemia and Cornelia) while the Japanese half is descended from a branch of the Japanese Imperial Family.
- Rai only learns about half his heritage. The Brittanian Army route has him learn of his ties to Brittanian Royalty, while the Japanese Liberation Front route has him learn of his Japanese roots. No route allows him to learn of his connection to both families.
- Compelling Voice: Compared to Lelouch's Geass which is based on eye contact, Rai's Geass is sound based. This backfires horribly when he accidentally sends his entire populace, including his beloved mother and little sister, to fight in a hopeless battle.
- Deal with the Devil: Rai made a deal with V.V. in order to gain the power of Geass. Using it, he was able to eliminate his father and half-siblings before seizing power. After his Geass went out of control and his beloved mother and sister (the ones he wanted to protect the most) perished as a result, Rai attempted to kill himself but was prevented by V.V., who pointed out Rai hadn't fulfilled his end of their bargain yet. V.V. opts to seal Rai away until the time is right.
- Despair Event Horizon: Rai crossed this in his backstory, when his Geass went out of control and the entire population of his nation marched to their deaths in battle, including his mother and sister, the ones he wanted to protect the most.
- Fantastic Racism: Rai, his mother and sister are victims of this in the backstory. Rai's Japanese mother, his sister and Rai himself were viewed as 'outsiders' and discriminated against. It got to the point where Rai decided to murder his Brittanian father and his half-siblings in order to seize power for himself.
- Humongous Mecha: The Knightmare Frames are the reason Brittania was able to steamroll over Japan. Depending on the route, Rai may wind up piloting one.
- King in the Mountain: Rai turns out to be this, as he was the ruler of a Brittanian territory who lost control of his Geass, and in despair put himself to sleep until he was reawoken by Brittanian forces. Whether or not he learns/ remembers this depends on the route.
- My Sister Is Off-Limits!: Unsurprisingly, this is Lelouch's attitude if Rai begins showing signs of romantic interest in Nunnally or vice versa.
- Power Incontinence: What happened in Rai's backstory. As the lord of his own territory, he tried to use his Geass to inspire his soldiers to fight to the death against an invading force. However, his Geass goes out of control and everyone who hears him (including civilians and his own family) march off to their deaths as well.
- Replacement Goldfish: Nunnally treats Rai like this at times as the story progresses and Lelouch begins spending less time with her (due to his role as Zero). Likewise, Rai initially treats Nunnally like a little sister (though that can change to a Relationship Upgrade).
- Spared by the Adaptation: The Brittanian Army and Order of the Black Knight Routes make it possible to save Euphemia from her accidental brainwashing and subsequent death. The Blue Moon and Ashford Academy Routes simply make the events that led to said brainwashing unlikely to occur, thus sparing her there as well. The Japanese Liberation Front spares JLF leader General Katase from being blown to smithereens by Zero.
- Super Soldier: A slumbering Rai was discovered by Brittanian forces under General Bartley. Bartley has Rai's body modified to handle the stresses of piloting a Knightmare and has knowledge and skills implanted into him. It's the reason why Rai, who has been in a magically induced coma for centuries, is able to adapt so quickly to the modern world.
The Geass Route provides examples of:
- Erased From Existence: What Rai inflicts on himself when he realises he's losing control of his Geass again. He puts himself back to sleep, but commands everyone to forget he was ever there.
- It doesn't fully work, as C.C. is totally immune and remembers him perfectly, while in the Lelouch ending he and the rest of the Student Council discuss the rumor of the helpful fairy who helped with the paperwork before vanishing.
- Poor Nunnally gets the worst of it, as she feels someone is missing, someone very dear, and she can't help crying because she can't remember who it is.
- Incurable Cough of Death: Rai claims to have this when his memories return and he realises he's losing control of his Geass again. It's the excuse he gives when he informs Zero and the other Black Knights he's leaving, claiming that he at least wants to see home one last time before he dies.
The Black Knights Route provides examples of:
- Battle Couple: Rai and Kallen can become one of these, with Rai even getting a mech with its own version of Kallen's Gurren Nishiki's Radioactive Wave Emitter Arm.
- Birds of a Feather: Hinted as to a major reason why Kallen is attracted to Rai. Like Kallen herself, Rai is half-Brittanian and half-Japanese, and she clearly enjoys having someone at school who is a fellow member of the Black Knights.
- Everyone Can See It: When Rai joins the Black Knights, he and Kallen spend a lot of time together, leading to teasing from the other Knights. Even before that, the students at Ashford Academy tease them about how much time they spend together. Kallen's undisguised happiness when Rai is proven to have Japanese blood doesn't help.
- He Is Not My Boyfriend: Kallen's reaction when the Student Council tease her about how close she's gotten to Rai. When Rai joins the Black Knights, she has this reaction when her fellow Knights tease her about him. No one buys her retort for a second.
- After Rai joins the Black Knights, everyone simply assumes he and Kallen are dating and are doing a piss-poor job of keeping it secret. Even Kallen only seems to be going through the motions when others mention it.
- Heroic Sacrifice: Rai pushes his Geass into overdrive in order to cure Euphemia of Zero's accidental command to exterminate the Japanese, and follows it up with mindwiping all the witnesses so Euphemia's reputation (and thus the very real chance of peace) are preserved. The stress almost kills him.
- Knight in Shining Armor: When Kallen and Rai get caught up in a terrorist attack involving Knightmares, rumors quickly spread in school about how Rai risked his own life to get Kallen to safety. Rivallz observes that even Kallen's most rabid fans can't find fault with him for it and are begrudgingly grateful to him.
- Moral Event Horizon: Should Rai choose to use his Geass to bring Suzaku over to the side of the Black Knights, an enraged Zero uses his own Geass to put Rai to sleep permanently for effectively brainwashing his best friend.
- Officer and a Gentleman: Guilford, Cornelia's personal knight, comes off as this during his battles against the Black Knights. He proudly announces his name, and when he defeats Rai in combat offers him the chance to surrender. When it becomes clear Rai will not take the offer, Guilford informs him he fought well before preparing to deliver the coup de grace.
- Red Oni, Blue Oni: Rai and Kallen have a relationship like this, as Rai is quite stoic while Kallen is very passionate. Bonus points for Rai piloting a blue Gekka while Kallen pilots the very red Gurren Nishiki.
- Rescue Romance: Ashford Academy students believe Kallen and Rai are in one of these when word gets out they got caught in a terrorist attack and Rai risked his own life to get Kallen (who, it must be pointed out, masquerades as a dainty wallflower in school) to safety.
- State Sec: The Black Knights ending has the Order of the Black Knights become a benevolent version of this, with Zero leading the Knights in protecting Euphemia's Special Administrative Zone from the shadows.
- Super Prototype: While not exactly 'super' or a 'prototype', Rai receives a pre-production model of the Gekkas that are piloted by Todoh and the Four Holy Swords. It is equipped with a pre-production model of the Gurren Nishiki's Radioactive Wave Emitter Arm. It isn't quite as powerful as Kallen's Gurren (which is more refined) but it's still a pretty powerful Knightmare frame.
- Worthy Opponent: Rai feels this way when he meets Guilford in battle. He apologises for not being able to give his name (in response to Guilford declaring himself) and admits he's honoured to face so great a foe.
- By the end of their fight Guilford sees Rai as this, praising him for fighting well even as he prepares to finish Rai off.
- Wrecked Weapon: During a battle, Rai can lose his customised Gekka. He goes into a depression as a result, with C.C. teasing him for looking like a knight who's lost his favourite horse and Kallen trying to cheer him up.
The Brittanian Army Route provides examples of:
- The Ace: Rai is a skilled pilot who manages to hold his ground briefly against one of Brittania's elite Knights of Round, and later proves to have good judgement under pressure. Almost all his superiors are impressed with him.
- Ace Custom: As part of the Experimental Unit along with Suzaku, Rai initially pilots a modified Sutherland (the most basic Knightmare in the Brittanian arsenal).
- Dangerous Deserter: In the Royal Guard ending, Cornelia wonders if Rai has become this before Nonette contacts her and informs her she's taken Rai back to the Brittanian homeland for treatment.
- A Father to His Men: General Darlton is this. Rai in particular considers him one of the greatest men he's ever met, due to his willingness to take people under his wing and the fact Rai once encountered him bringing toys to an orphanage.
- At one point of the Royal Guard route, Darlton tells Rai that if they'd met before he'd joined Cornelia's Royal Guards, Darlton would've adopted him as his son (since Rai's military profile notes he has no family left in the world).
- The Friend Everyone Likes: Rai gets this treatment if he accepts Cornelia's offer to join her Royal Guards. The unit captain Guilford (Cornelia's personal knight) is impressed with his skill as well as the fact Cornelia personally recruited him. General Dalton also praises him after his success in an operation. He even impresses Nonette Ingram, the Knight of Nine.
- Cornelia herself sometimes expresses irritation at how much her subordinates like Rai, thinking that he might get a swelled head.
- Mid-Season Upgrade: While Rai initially pilots a customised Sutherland (that boasts improved speed and response time), he later receives his own version of Suzaku's Lancelot, the Lancelot Club.
- Praetorian Guard: Rai can get the option of becoming one of Princess Cornelia's Royal Guards if he sufficiently impresses her.
- Short-Range Guy, Long-Range Guy: Rai's Mid-Season Upgrade the Lancelot Club has this relationship with Suzaku's Lancelot. While the Lancelot's primary weapons are its MSV swords with a rifle as a backup, Rai's Lancelot Club's primary weapon is its variable rifle (which can switch between a sniper mode or an assault rifle mode) and its MSV are the backup weapons.
- Suicide by Cop: What Rai tries to pull when he realises something is terribly wrong with him (his Geass is going out of control). He attempts to force Nonette, the Knight of Nine, to kill him, but she quickly knocks him out.
- Those Two Guys: The Experimental Unit ending has Rai and Suzaku develop a reputation as this, becoming the White Knights and faithful guardians of Princess Euphemia and her Special Administrative Zone (a recreated Japan).
- Tsundere: Adorably, Princess Cornelia can act like this at times.
The Ashford Academy Route provides examples of:
- The Heist: In order to rescue Milly from an arranged marriage, the Student Council pulls together to demonstrate how unsuitable the match is. Rai is recruited to play the role of Knight in Shining Armor.
- Mood Whiplash: The route itself is fairly light-hearted, but the ending involves a terrorist attack and a hostage situation. Rai is forced to resolve the situation by using his Geass to make the terrorists commit suicide, and then uses his Geass on the witnesses to forget what had happened. He flees shortly thereafter and is never seen again.
- Wholesome Crossdresser: During the school festival, Rai can get roped into playing dress up. Lelouch or Milly can wind up joining him if their relationship values are high enough.
The Japanese Liberation Front Route (PSP version only) provides examples of:
- Amicable Exes: After Rai's defection from the Black Knights, his relationship to them is something like this. He and Kallen get along well and she makes it clear she'd love for him to come back. She's overjoyed should Rai decide to join Tohdoh and the Four Holy Swords in allying with the Black Knights.
- Arranged Marriage: Kaguya and Rai can wind up in one of these when the Kyoto Six learn that Rai carries the blood of an extinct Imperial family. Unusually, it's Kaguya who does the arranging, even forcing the Kyoto Six to go along with it.
- Armor-Piercing Question: When Zero has Rai detained, he scolds Rai for disobeying orders and going to the aid of the JLF. He tells Rai that everything that happened at Narita was part of his plan, to which Rai coldly points out that that means the losses suffered by the JLF and how close they came to annihilation was also part of Zero's plan. A sputtering Zero can do nothing more that cut the conversation short and leave.
- Defector from Decadence: Rai's reason for abandoning the Black Knights and joining the JLF is his disgust at how Zero is perfectly willing to sacrifice the JLF soldiers as part of his strategy. The breaking point is when Zero outright orders the Black Knights to ignore JLF forces who are in trouble, and later says everything that happened during the battle was part of his plan. Rai points out this means Zero fully meant the JLF to suffer heavily losses, which destroys his faith in Zero.
- Rai can wind up doing this again should he side with Tohdoh and be abandoned by General Katase and the JLF, accepting Zero's offer to rejoin the Black Knights.
- Didn't Think This Through: When Rai goes to join up with the JLF, their commander General Katase inquires why he wants to join them. His bodyguards take aim and Rai realises that there's something suspicious about a member of an upstart resistance group that almost took out the JLF in the course of their own plans wanting to join. Add to that the fact said member just happened to rescue some of the JLF's most revered soldiers during the course of the battle adds to how convenient it is. Rai is forced to resort to using his Geass to get out of the mess.
- Dirty Coward: For all his talk, General Katase proves to be this during the defense of Ishikawa, when he immediately orders a full retreat when his headquarters comes under attack by Guilford. This is despite the fact the JLF are actually winning and have both Darlton and Cornelia surrounded. His order to retreat throws the JLF into disarray, letting the Brittanians rally and counterattack.
- Fire and Ice Love Triangle: Rai can wind up in one of these with Kallen (fire) and Chiba (ice).
- Alternatively between Kaguya (fire) and Chiba (ice).
- Fond Memories That Could Have Been: Rai has this reaction a lot with regards to Kallen after his defection from the Black Knights. His first thought when he's informed he has noble blood from an extinct line is to think, "Kallen would've been overjoyed to hear this." Later, when he is given his customised Gekka, he is immediately reminded of Kallen due to the Gekka's Radioactive Wave Emitter Arm being the same one equipped on Kallen's Gurren.
- I Did What I Had to Do: Zero's reasoning as to why he was willing to sacrifice members of the JLF. Rai has no problem with soldiers dying in battle, but the fact that Zero's plan actually called for the JLF to be slaughtered is what causes him to defect.
- Should Rai follow Tohdoh and the Four Holy Swords in being abandoned by the JLF, this is his reasoning behind accepting Zero's offer to rejoin the Black Knights.
- Master of the Mixed Message: Chiba in a nutshell. She admits being impressed with Rai, but treats him with a stoic professionalism even if Rai expresses interest in her. However, should Rai grow close to Kaguya or Kallen, Chiba asks him what he thinks of them. The way she asks hints she's somewhat jealous.
- Nice Job Breaking It, Hero!: Zero's poor choice of words when dressing Rai down for disobeying orders causes Rai (who Zero acknowledged as being a potentially useful tool due to his skills and intelligence) to defect. Worse, the JLF soon carry out blood tests that show that not only does Rai carry noble blood, he's actually part of an extinct Imperial line. That proves to be a tremendous morale and political boost to the JLF.
- Precocious Crush: Kaguya can develop one for Rai, due to him being a young, attractive noble who bravely fights against the Brittanians on the front lines alongside some of the JLF's greatest heroes. Rai can reciprocate or gently let her down.
- Spanner in the Works: Rai's opposition to Zero costs him the full support of the Liberation Front's backers the Kyoto Six, costing him the resources and support he enjoyed in the anime. As a result, the Black Knights are nowhere near as well-equipped as in the anime.
- Furthermore, Rai's interference ensures the Liberation Front is still a viable resistance and aren't forced to combine with the Black Knights.
- Star-Crossed Lovers: A variation between Rai and Kallen if her relationship values are high enough when Rai abandons the Black Knights. While the two of them are attracted to each other, Kallen believes in Zero while Rai distrusts him.
- We ARE Struggling Together: The Japanese Liberation Front and the Black Knights don't get along due to differing methods. They are also political rivals, as the Kyoto Six (the main backers of resistance groups) can't decide who to throw their full weight behind.
- The Kyoto Six actually lean more and more towards the Black Knights as time goes on, due to their increasing disillusionment with Katase's leadership of the JLF. His willingness to ally with the Chinese Federation (effectively inviting them in to take Brittania's place as Japan's overlords) is the last straw.
The Blue Moon Route (PS2 version only) provides examples of:
- Lighter and Softer: There's no combat here, and it mostly plays out like a typical light-hearted school anime. Characters who never joined Ashford Academy like Euphemia and Kaguya are transfer students.
- Took a Level in Jerkass: Kaguya, who in every other route (and the original anime) is an adorably sweet young girl, becomes quite belligerent towards Rai in the Blue Moon Route when she becomes a student as Ashford Academy.