There's two bad things about mc, first why TF would you take a bath with your sister, that is 10 YRS OLD!? Second, stop being a bum don't let a little kid control you, make her grow up.
Ok, i may not know a lot of japanese culture and traditions, but i'm pretty sure that bathing with your 10 year old sister is not acceptable in any circumstance. The hell is wrong with this guy.
Whatever good this story has along the way, I don't think I can bear reaching because I can't tolerate the fuggin little sister. She's worse than overbearing parents. I typically buy into the initial premise, but I really REALLY can't take that brat anymore, I'm sorry.