Tenchi Forever!(1999)

Overview:

One day, Tenchi disappears in the forest near his house. Six months later, Ayeka and Ryoko locate Tenchi living in a city, but with a mysterious woman. What's more, Tenchi appears to have aged several years. Whenever Ayeka and Ryoko catch up to him, he disappears into thin air, apparently existing in a fabricated alternate dimension where he has no knowledge of his past.