TSUMA TO FUTATABI KOI SURU MISSION

An alien takes over the body of a married man to study human reproduction. There's just one problem: the couple's relationship has gone completely cold. Getting them into bed together is the least of his worries: understanding the human wife's heart may prove to be a greater mystery than the universe itself. (Source: Harta, translated) — Description from AniList community (anilist.co).