Isekai Kaeri no Daikenja-sama wa Sore Demo Kossori Kurashite Iru Tsumori desu

Saito was reincarnated into another world at the age of 15, where he rose to become the Great Sage and defeated the Demon Lord. Soon after this victory, the portal linking the other world and the real world opened, allowing Saitou to return to Japan with the powers of the Great Sage. However, 19 years had passed in the real world during his absence. Reunited with his childhood friend Kanako, now a single mother, Saito finds himself drawn back into life in Japan. But it appears that someone is threatening Kanako's life. Thus begins the story of the Great Sage, who wishes for a peaceful life after returning from another world!