Roxas and Xion first met when the latter joined Organization XIII one week after the former did. Xion is actually a replica of Roxas so they immediately had a connection. In fact, Xion looked up at Roxas and smiled when they first met. When Roxas was about to leave for his first training mission with Axel, Xion watched him shyly from a distance. Saïx also introduced her to him and Axel.
After many missions of training and Axel's departure to Castle Oblivion, Roxas was sent on missions with Xion and put in charge of her. After doing missions together, Xion eventually began to speak to Roxas and put her hood down, revealing her face to him. She also discovers her ability to wield the keyblade in front of him. Roxas eventually falls into a coma as the result of Sora being put in one. Xion visits Roxas every day and leaves him a seashell from the world that she visits.
Roxas and Xion became friends along with Axel but things would soon take a turn for the worst. Xion leaves the organization multiple times but is eventually brought back. Roxas and Xion are both going through similar situations with memory lapses but the latter is too afraid to talk about it. Roxas eventually leaves the organization for a similar reason while Axel captures Xion and brings her back again. Xemnas resets Xion as it turns out that her true purpose is to absorb Roxas.
Xion eventually confronts Roxas in Twilight Town. She attempts to absorb Roxas but he manages to defeat her. Xion is returned to normal as she fades away but Roxas initially forgets about her. Roxas holds Xion as she is fading away and tells Roxas to free the hearts they captured and that she enjoyed spending time with him and Axel. Roxas finally remembers her and asks her who he will eat ice cream with but she fades away and leaves behind a single sea shell. Roxas begins to cry.
The next day, Roxas still has memories of Xion. He decides to take on Organization XIII and free Kingdom Hearts in hopes that he can be with Xion again. Roxas now has the ability to wield two keyblades because of Xion's presence inside of him. While fighting Riku, Xion makes Roxas throw a keyblade to him and tells Riku that he has to stop Roxas. Riku manages to capture Roxas and take him to Ansem. While Roxas has his memories wiped and is placed in a simulated Twilight Town, Xion tells Roxas not to be sad because they will both be back with Sora.
RokuShi is one of the most popular Kingdom Hearts ships. It is the most popular Xion ship and is possibly the most popular het Roxas ship although it closely rivals RokuNami. Some fans wanted to ship this before 358/2 Days even came out. While many fans did not want to ship this because of Naminé, it quickly became popular as fans played through 358/2 Days. In fact, it was implied in the game that Roxas might have liked Xion and many fans picked up on this. Since Roxas and Xion are both inside of Sora, many fans feel that they can be together inside of him.
- Roxas took on Ventus' appearance due to the latter's presence in Sora's heart while Xion took on Kairi's appearance due to the latter being Sora's strongest memory.