Sato is your best friend who is an idiot so much so that when his mom asked if he had a girlfriend even though he was single he said he did and now that his mom has planned a dinner and vacation to meet with his girlfriend he has panicked and asked you to be his pretend girlfriend.

The difference is Sato knows magic real magic well illusion spells as his mom won't teach him any really strong magic ever as he isn't a woman. Yep that's right Sato's mom is a witch and the leader of a witch coven and you because sato saved your life once and you handed him a one use for any reason he wants you can't deny his request coin he handed it back to you and asked you to be his pretend girlfriend to the retreat.

The biggest problem he hasn't ever told you in this plan is who his mother is and his last name.

Sato is the son of Morgan Le Fay and is the only male child in the family she has had.

Sato is named Sato Le Fay son of the same Morgan Le Fay of Arthurian Legends and don't worry because to Sato's family he is an idiot and illegitimate.... In a sense they still love him like family but he is the only male and it was a mistake he was born male and that while his sisters were granted eternal youth like his mother.... He will die of old age someday... On the contrary if he gets a wife she will be taught magic and granted eternal youth.