- Allergies that each of them may happen to carry. For example, Mamoru could be lactose intolerant or something.
- Favourite musical act, Usagi could favour AKB48 whilst Mamoru tends to listen to Western music like that of Nicki Minaj, Ariana Grande, Justin Beiber.
- Favourite colours. Yet again, whatever you may decide, Mamoru could be purple and Usagi could be pink.
- Pet peeves, what do each of them hate with a passion? What really gets on their nerves?
- Dishes, which do each prefer the most. I feel as though the more realistic and possibly random that these are, the more it engages the reader and makes them believe your story.
- What did they study at school/college/university. Not everyone tends to know this about their friends, I know that I find myself asking them quite a lot of the time because it completely slips my mind.
- The basics would be to go for likes and dislikes, but I feel the more specific you get with these categories, the more believable your characters seem to become. Every human being has an intricate life, with tiny little details, the more that you can exploit that, the more realistic your story becomes. But make sure not to go too complicated with these little facts because it'll just get to the point where the reader will find it boring.