(If the background link isn't detailed enough, I'll add to it.)

Personality: Riku is a timid, quiet boy but he has a kind and gentle nature. He's friendly, and not one to judge others, despite any differences they have. This is seen by him befriending Mui, a young girl who lost her leg in an incident, and his devotion to continuing to treat Saya as his big sister, even after finding out she was a Chiropteran and not human. He cares about his siblings very much and always works to bring them closer.