Riku is appointed team leader of the Seagulls in the children's game of Island War, with Sora and Selphie as his teammates. Even though Selphie defects to the other team, Riku and Sora easily defeat Tidus, Wakka, Kairi, and Selphie.
After the battle, Riku collects materials for the raft, then has a race with Sora. He begins to tease Sora, leading both of the boys to admit they have a crush on somebody, although neither elucidates further.
That evening, Riku, Sora, and Kairi discuss the raft trip and other worlds. As the children head home, Riku tosses Sora a paopu and is dejected when Sora throws it away.
With two days left until the raft is finished, Riku is abused by his homophobic parents. He goes to Sora's house for safety, refusing to tell Sora about the reasons for their cruelty. Soon, the two begin to tease each other, and Sora falls asleep in mid-conversation on top of Riku.
The next day, Riku easily bests Tidus, Selphie, and Wakka, then has a race with Sora. As part of his Plan A, Riku suggests the reward for the race be to share a paopu with Kairi.
Sora wins, but Riku claims that his heightened stakes were just a joke. During a second race, the boys end up falling into the water below, and Sora catches Riku looking at him with one of his "stares". Sora goes to get a towel, returns with Riku's paopu, and confesses his love. The two boys share the paopu and have their first kiss.
Riku and Sora continue to kiss and almost go all the way before they are interrupted by Tidus. After Tidus leaves, the two discuss their relationship, Riku's "Plan A", and Kairi. Later, Riku encounters Selphie, who reveals that she knows about him and Sora, and considers them to be meant for each other.
Riku and Sora return to Sora's house together, where Sora's mother Seiya allows the boys to eat alone in Sora's room. After dinner (and a little play), they return to the play island.
Although planning to separate Sora from Kairi, Riku accidentally overhears their conversation. Kairi expresses concern at Riku's manner and suggests leaving him behind on the raft trip, before quickly clarifying that she is "kidding". Neither Riku nor Sora is amused. After standing up for Riku, Sora goes to the secret place, where Riku follows him. Kairi witnesses their intimacy and interrupts, feeling hurt that she is suddenly a third wheel. Although she leaves quickly, Sora reassures her that she can come with them on the raft if she shows up. When he returns, he and Riku share an intimate moment that is interrupted by Sora's grumbly stomach.
The darkness assaults the Destiny Islands and Riku is suddenly swallowed by it. A voice urges him to call "the key" to himself and to open the door, and the darkness around Riku dissipates. Riku heads for the mysterious door in the secret place, which is now adorned with a large keyhole. He is unable to figure out how to summon "the key", and soon Kairi arrives, looking for Sora. The Heartless begin to manifest. A mysterious man explains the Heartless's arrival, speaking of "two strong hearts, and a pure heart". The darkness envelops Kairi, and the mysterious man sends Riku to the paopu island, where he waits for Sora.
Riku waits, ignored by the Heartless. Sora arrives, asking about Kairi, but Riku waves aside the questions and urges Sora to join him in going through the darkness to other worlds. Just before the darkness swallows them, Sora takes Riku's hand.
Riku awakes on cliff surrounded by water. He sees Sora nearby, but as he approaches, Sora becomes a sort of demon, emitting a horrific sound and sprouting two black wings. Both boys fall off the cliff, and Riku wakes suddenly.
The two boys find themselves in a town covered in snow. Soon, Heartless emerge from the ground and the boys are forced to run, but when Sora trips they are attacked. Riku is surprised to find that now the Heartless are focusing on him instead of Sora. They are saved by a boy on horseback who offers to take them back to his camp.