NAZOTOKINE

Tokine Amino is the company president's secretary at the advertising agency TEN2. One day, she's cleaning the conference room before a meeting with a famous animation company when she finds herself surrounded in light and then is unable to leave the room. As an added a bonus, a creature named Hacchin appears like a ghost and tells her she must solve the mystery to be able to exit. (Source: Anime News Network) — Description from AniList community (anilist.co).