Sonic's pin, which he had acquired prior to entering the world of Remnant, transforms into a saber called "Hyper Drive". It has the longest reach of any of the SMSH team's weapons, and can even retrieve objects without damaging them. But when fully activated, it can slice a Grimm in half....if it doesn't get burned up by the actual intensity of the blade itself!
Sonic's semblance is his speed. At first, he thought he just wasn't affected, but seeing Ruby's speed made him realize that his current quickness already made him special to the team.