Tamagotchi Mesutchi (1997)

According to Mikachu's logs, gendered Tamagotchi characters were a new discovery made while the Tamagotchis were living on Earth, and had not previously existed on the Tamagotchi Planet. According to her, the Osutchi and Mesutchi characters starting being born when couples began sharing their Tamagotchi pets with each other. As Professor Banzo often get flustered about the concept of love, Mikachu spearheaded the research on them. Since the original "Tamagotchi HOUSE" model was inadequate for caring for a growing Tamagotchi family, Banzo and Mikachu together developed the "Osutchi HOUSE" and "Mesutchi HOUSE"