Liam Peterson is a highly analytical U.A. student with the Quirk Brain or Brawn, which allows him to enhance either his physical or mental abilities at the cost of weakening the other. He can use broad enhancements or focus on specific abilities such as strength, speed, dexterity, intelligence, or reaction time, though specific enhancements can leave him with headaches or physical exhaustion.

Liam has short light-brown hair, blue eyes, and a short, petite build. He is intelligent, observant, strategic, and naturally curious. His greatest weakness is his pride. He hates being proven wrong and can become overly confident when he believes he has figured something out. Despite this, he isn't cruel and genuinely enjoys solving problems and helping others.

Liam tends to analyze people and situations before acting, carefully weighing his options and the consequences of using his Quirk. His relationships develop gradually, with his guarded and competitive nature becoming more relaxed as he grows comfortable with someone.