18+ Elf no Oshiego to Sensei

Kobayashi Hiroki is a teacher for a tribe of elf students who came from another world. No one is sure why the world where the elves come from collides with our world. Hiroki however has fallen in love with Laranoa, one of the otherworldly students, which is strictly forbidden... So they act on their love in secret whenever they get a chance to be alone.

(Source: TMDB)