If you're looking for manga similar to Demon Slayer: Kimetsu no Yaiba - The Flower of Happiness (Light Novel), you might like these titles.
Tanjirou and the group have completed their rehabilitation training at the Butterfly Mansion, and they arrive to their next mission on the Mugen Train, where over 40 people have disappeared in a very short period of time. Tanjirou and Nezuko, along with Zenitsu and Inosuke, join one of the most powerful swordsmen within the Demon Slayer Corps, Flame Hashira Rengoku Kyoujurou, to face the demon aboard the Mugen Train on track to despair.
Somewhere between magic, art and science exists a world of alchemy. And into this world travel Edward and Alphonse Elric—two brothers in search of the Philosopher's Stone, the ultimate alchemical treasure!
It was supposed to be just an ordinary, C-rank assignment - but nothing about ninjutsu is as simple as it seems... Squad Seven's latest job is a real snore: escorting a young, cowardly leader named Shibuki back to the remote Hidden Waterfall Village. They arrive without a problem, but get stuck cleaning the village pond! While Naruto and his pals pick up the trash, Kakashi is called back to his home village on urgent business.