Lewin didn’t seal Rin's powers in his sword. He’d wanted Rin to start learning as early as possible to control them.

Rin doesn’t even possess the Kōmaken and has some Aria training under his belt because of it. 

Although he is excellent at wielding every kind of sword thanks to the Knight lessons Lightning’s friend’s friend gave Rin. He knows four out of five Meisters. Aria is the one he doesn't have because he's too lazy to memorize the whole damn Bible and he has a secret fear that he will find his own fatal verse and accidentally kill himself.

He's about to get his doctor Meister and studies for it with Yukio and Shiemi.