Isekai Kaeri No Daikenja-sama Wa Sore Demo Kossori Kurashite Iru Tsumori Desu summary:
Saito, who reincarnated in a different world at the age of 15, becomes a great sage and completes the subjugation of the Demon King. Immediately after, the door connecting the different world and the real world opens, and Saito returns to Japan with the power of a wise man. However, 19 years have passed in Japan. Saito, who is in a state of Urashima, met Kanako, a childhood friend who became a single mother. There seems to be an enemy aiming for this life that is kind of something ... The slow life Wannabe story of the wise man who came back from another world begins!