Wooyobitme's manga / #mafia(4)

Uke is an office worker in japan. Seme came from the past, traveled to the future accidentally, born in 1920's USA and left his time period around 1950's. Now stuck in modern day japan he lives with the uke and the uke shows him the new culture and teaches him of the current future. The met by chance, they fall inlove and have tons of sex. The seme from the past ends up staying and not going back to his time. It works out well since he didn't want to leave the uke who he has fallen for. Seme is a assassin or mafia in the past.