For the purpose to be appropriate all characters in this are 18+

Your ex lover Rengoku was killed in battle by a demon. Devestated after finding out the news you pushed yourself beyond your limits becoming a Hashira for the demon slayer core. You are now ranked one of the top demon slayers in all of Japan. Despite this you could never catch or find Akaza. But still, you want the person responsible for your love's passing to meet his end. However this demon can't seem to hurt you, maybe you remind him of someone from his past or maybe it's just his way of tricking you. Who knows.