Riku is a rather prominent character in the manga series Kingdom Hearts. The manga itself is based on the video game series by Square-Enix and Disney. In the story, Riku plays the role of the "rival" character. In the beginning, he is the best friend of Sora (the story's hero), but the two of them are also always competing with each other. Throughout the story, Riku is manipulated into using the power of Darkness and eventually fights Sora.

Possible Spoiler Warning for the KH1 and Chain of Memories video games plus the KH1 portion of the manga!
When I first began the Kingdom Hearts video game, I liked Riku. In fact I almost liked him as much as Sora. But as the game progressed, my respect for Riku dwindled. I thought he was whiney and annoying, and I was angry at him for believing obvious Disney villains instead of trusting his best friend. But then came Chain of Memories, and from the moment you first start the Reverse Rebirth portion (the version of the game you play as Riku), I realized that Riku was back to being that sarcastic, funny, badass guy who appeared in the beginning of the first game. Riku's attitude toward the various villains he meets in Chain of Memories always brought a smile to my face. He had such a snarky way of talking to them, and his dialogue was great. Also, playing as Riku lets you see the story from his perspective, and it was refreshing to say the least. Oh yes, Riku was cool again.

In the manga, Riku's portrayal is very loyal to the game (much more so than Sora's). But we get the added bonus that his view is more clearly shown in the beginning, instead of leaving us to speculate on why he turned to the Darkness. I think it's an excellent addition to the story, showing more of Riku's feelings and perhaps fleshing him out a bit.
End Spoiler Warning!

I chose the title "Forces" for the fanlisting because a song of the same name (an insert song in the "Berserk" anime series) strongly reminds me of Riku and his struggle with his own darkness. You can view the haunting translated lyrics here. It's far more beautiful to actually listen to it, so try to track it down if you can!