The Shut-In Sage

A once-ordinary teenager is hurled across countless dimensions for 10,000 years. In each world, he masters every form of magic, hoping the next portal will lead home. When he finally returns, the world has changed into one of guilds, hunters, and systems, while time dilation restores his body to his teenage form. He wants a peaceful, quiet life, but a side effect of his journey has made him a shut-in who watches hunter streams and cannot resist teaching them.