Kingdom Hearts - Riku

Riku is the best friend and rival of Sora, and best friend of Kairi. He is one of the 3 main characters of Kingdom Hearts. His name is derived from the Japanese word for 'land'. He and Sora share a fierce but good natured rivalry, competing over who is stronger in battle as well as over Kairi's affections, among other things. All three of them, as well as the other children that live on the islands, spend most of their time on the smallest island, acting as their own personal playground.

However, things take a drastic turn on the night before their journey. Riku, likely unable to leave the islands without knowing the truth, opens the door in the secret place and the Heartless, beings of darkness, invade the islands, seeking out the world's heart. Both afraid that a storm would destroy the raft, Kairi and Sora also set out for the island. Sora finds Riku first. However, while Sora is concerned for his friend's safety, Riku is only obsessed with finally escaping the island. Darkness surrounds the two, and Riku disappears into it, while Sora gains the Keyblade.

Riku confused as to why Sora was able to regain the Keyblade. A mysterious voice somehow contacts him from the Darkness, telling him that only one with a stronger heart can claim the Keyblade, and Riku himself was weaker than Sora. However, the mysterious voice, now slowly taking a shape, presents Riku with an offer he can not resist, a Keyblade of his own. Under the influence of jealousy and rage, Riku agrees to become one with the Darkness, only to become possessed by the mysterious voice itself.

Riku, calling himself Ansem, the Seeker of Darkness, later confronts and battles Sora (who is cut off from Donald and Goofy) at the Final Keyhole. He hopes to release Kairi's heart from within Sora's, so that she, being the final Princess of Heart can open the Keyhole. He fails, but Sora impales himself anyway to save Kairi. With Sora gone, Xehonart's Heartless attacks Kairi, Donald, and Goofy, but they are saved by Riku, who is using the last of his strength to hold the dark powers of his possessor off.

Riku's rejection of Xehonart's Heartless leads to an internal struggle between the two, which Riku ultimately loses. This causes Riku to lose control of his body once more, while Xehonart's Heartless gains it fully.

A newly restored Sora, along with Donald and Goofy, eventually make their way to the End of the World, the home of the heartless. There they once again confront Xehonart's Heartless and defeat him after a series of battles at the Door to Darkness. Riku is then restored, and appears on the other side of the Door to Darkness, aiding Sora in closing it, but unable to cross it, as only pure darkness can go back and forth through the door. Waiting to enter the Realm of Light are thousands upon thousands of heartless, who only cause further problems for the two friends. However, King Mickey, appearing for the first time in the game, ward them off, with a powerful golden colored Keyblade. The King and Sora then proceed to close the door, Sora on the outside, Mickey within. Riku is stuck on the other side of the door with the King....

For more detail about Riku, please refer to >>
http://kingdomhearts.wikia.com/wiki/Riku