You really kind of need to see Demon Slayer: Kimetsu no Yaiba's movie. No, that's not exactly right. You absolutely need to see it either while it's still making its run through theaters or it hits digitally later this Summer. Picking up immediately after the final moments of the first season's final episode, Demon Slayer -Kimetsu no Yaiba- The Movie: Mugen Train serves as a bridge between what came before and what's coming next in the anime. Because it directly adapts Koyoharu Gotouge's original manga series, it's an incredibly important piece of the series' puzzle.