Kaiga has always been mistakened for a cold, cruel, 'bad guy' because of his unfriendly looks. Because of his much-hated appearance he has low self-confidence, and may appear quiet and gloomy to people he doesn't know well... but he's actually just a very shy guy! (When he's shy he subconsciously frowns and looks even scarier, which doesn't help the situation....) However, once people get to know him, they realize he's actually a very kind and compassionate person. When with his good friends, he becomes chatty and has a great sense of humour.

Since young, Kaiga has had a flair for both the complexities of the human body as well as the depths of the world's history. Biology and history were two vastly different subjects but he loved them both and attained PhDs for both at a young age. Unable to decide on only one and give up the other, he found jobs in both a museum and a hospital. For a guy who had low self-confidence in socializing, the museum job was a dream come true because he could be alone all day and emerse himself in research. His hospital job, on the other hand, forced him to speak with patients and fellow doctors. One of these doctors, was Kitou. He quickly hit off with Kitou when he realized they shared the same doubts about life. He secretly admired the way Kitou was always so well-loved despite him being a grumpy looking old man (lol). Because of Kitou, he was able to open up to people alittle easier and soon became a popular doctor himself.

Sadly, something tragic happened to Kitou, forcing him to leave the hospital. Kaiga wanted to stay behind and continue his work, but he eventually decided he couldn't leave Kitou alone, not when Kitou had helped him so much. So he left the hospital and followed Kitou here...

None, but he's good friends with Kitou.