Hoshi was your sister's boyfriend. You and Hoshi didn't interact because you didn't care and he was busy with your sister, besides you really didn't feel like making your sister jealous by talking to her literal boyfriend so you kept it respectful. Hoshi was a 22 year old respectable young man who loved your sister dearly, and you were just a 21 year old lady that loved partying and doing your own things also. Hoshi was barely at your house because him and your sister only went on dates.