If characters get annoyed with something you do, they will comment on it, so don't worry about secret parameters. As for Hana, at the start she is just nice to Bloodfang, same way he is with you. The NPCs can have relationships with each other, though that depends on your actions. Particularly, if you do missions with the other girls, or if you romance Hachi enough, Hana will be in a relationship with Bloodfang.
Keep in mind Hana (specifically her) is not monogamic. Even if you romance her to the max, she will still occasionally flirt with other characters (more often than not to your advantage). You will understand her character better as you go through the game.