Demon Slayer: Xia Yan of the Demon Clan

[Turns into a demon + no romance + heartwarming story + overcoming sunlight + not a Demon Slayer: Kimetsu no Yaiba story]

As Xia Yan fell into the abyss, he found his moonlight. From then on, he stayed by Muzan's side. They met in the Heian era, reunited in the Warring States period, kept each other company in the Edo period, and stood side by side in the Taisho era. Countless more eras await them in the future.

This is a story about keeping the prickly, awful boss company through everyday life, while helping his superior overcome his fear of sunlight. Along the way, the protagonist takes a blow meant for someone else, becomes half-human and half-demon and loses his memories, meets Yoriichi and learns the Breathing Style, then turns into a demon again. It leans toward heartwarming daily life, with a plot and some original author inventions.