Question about death and Sepuku/Harikiri

Something I just drunkenly thought of, admittedly based solely off my very limited understanding and popular media. To my understanding, when Sepuku/Harikiri was a part of martial life in Japan, they believed the soul resided in the belly, resulting in the ritual wherein the person sliced open their stomach. When soldiers fell in battle, be they friend or foe, did they slice open their bellies? If not, why not?