Talk to mabel, get sent to a journey to raise your STR to level 2, find the 3rd diary, talk to mabel. Congrats, you raised relationship.(Note. REALLY. REALLY oversimplified)
Thanks? According to the creator, incest is optional. That was the intended query. That's different, no?
You can give a custom name for your relationship with Mabel at the start of the game, she's your "best friend" by default.But if you are using an old save and forgot what you set before, unfortunately there's no way to check it for now.