Context: Todoroki Shouto 轟焦凍 has both cold and heat abilities, which come from the sides of his body: from the right comes cold, from the left comes heat.
sentou ni oite
netsu (hidari) wa zettai
tsukawanee 戦闘に於いて熱（ひだり）は絶対使わねえ In battle [I] absolutely won't use heat (left).
In other words: he said he won't use "heat," netsu 熱, by saying he won't use the "left" side, hidari 左.
