Ore Maou! ~Kudake Chitta Tamashii (Ore) no Kakera o Shuushuu Seyo!~

I, Ouma Ryousuke, work as a teacher who trains demon slayers. However, I am a former demon king! My soul was sealed in a shrine in the distant past, causing me to lose my power. Somehow, only the core of my soul managed to survive, and I now live quietly as a human.
But if I can take in the remaining souls sealed in the shrine, I should be able to resurrect as the demon king! ...However, no demon can approach the shrine. That goes for me too.
This year, there are students in my demon slayer class who have decent potential but are very poor in execution. I successfully broke the barrier of the shrine in exchange for exempting these students from supplementary classes. The seal was released, and the souls were freed.
However, the impact was so great that the souls shattered into pieces and flew off to various places. I am using my students once again to collect the fragments and return as the demon king...