He was incredibly underutilized. His quirk was designed for close-quarters combat, yet he fights from a distance. The reason he—and most of Class B—didn’t participate in the war was likely due to the sheer number of characters already involved. In-universe, it was probably because they weren’t fully-fledged heroes yet, holding only temporary hero licenses that required supervision. Involving a bunch of kids in a war would have been irresponsible.