Jimina Ken Sei Wa Sore Demo Saikyoudesu

Story:

A Japanese student named Sansui died because of God's mistake and was teleported to another world. He announced that he wanted to be "the strongest", so he received a letter of recommendation from God to the Sage and studied for 500 years. When he reached a level where he could be called the "strongest" by the standards of ordinary people, he picked up a child near his training ground, and that's where his adventure in the other world finally began. He has simple training, simple techniques, his weapon is an ordinary wooden sword. It's the strongest, but it looks ordinary. So, the St. Sword's battle journey has just begun.