Action Monster Big Movie

Following a decline in the amount of monster movies created, Monty, a director who is obsessed with the monster movie genre, becomes unsure about his persistence—he never expected that one day an actual monster would appear in front of him! In order to fulfill his dream, Monty decides to cooperate with the demon girl Leah and help her shoot a demon themed movie. However, as the shooting progresses, Monty discovers that things in the other world are closely related to him. Source Bilibili​