Doing nothing => F-rank => freedom.
Run around, doing a lot of things and beat every A-rank => S-rank=> "probably" freedom.
I don't know how he can become a sage in his last life with his IQ
![haa :haa: :haa:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
He can even quit being an adventurer and has a live by selling monster materials.