Otome Isekai is a sub-genre of Isekai where the main character(s) are in some way transported to another world that resembles an otome game.

Isekai means "other world" in Japanese. Isekai stories are those where the protagonist goes to another world. Things like Escaflowne, Sword Art Online, even No-Game No-Life are all forms of Isekai. Otome means "maiden" and "otome games" are a type of dating-sim visual novel game for girls and women. The goal is to make choices to navigate various story routes to win the hearts of different capture targets.

It is essentially the girly version of the modern shounen isekai that goes in the direction of female wish fulfillment. Instead of stuck in an action game, she's stuck in a romance novel or romance game. It is almost always "died and reborn there" rather than the sort of "stuck" we see in Sword Art Online or the "teleported" we saw in the 90s. In general, otome isekais contain almost all of the following tropes:

1. The Main Character (MC) has foreknowledge of the events to come.
2. Our Main Character is usually a villainess.
3. Our Main Character almost always wants to avoid the "bad ending."
4. The setting is Lords and Ladies.
5. The Story is about relationships.
6. It is written for the "Female Gaze".