The commercial for WFS and Bandai Namco Entertainment’s upcoming TenSura mobile game teases Rimuru having a supposed daughter. The game, translated as That Time I Got Reincarnated As A Slime: The Saga of How the Demon Lord and Dragon Founded a Nation aired a commercial promoting its pre-registration. You can watch it here:
Towards the end of the commercial, we can hear Rimuru saying “Huh, my daughter?!” while the text “Rimuru’s daughter?!” appears on screen, together with the person in question.
The anime opening for the game gives a clearer view of the supposed daughter:
She has two antennae on her head, together with clothes that bare her midriff. You can see her turning around to meet Rimuru in the game’s anime opening below:
Rimuru never had a daughter in the That Time I Got Reincarnated as a Slime light novel. In fact, she is an original character made for the game, Shinsha. According to her description below, she is Rimuru’s self-proclaimed daughter who possesses abilities similar to Great Sage and Predator. Currently in the game, she is one of the enemies that players will encounter as part of the story.
You can read more about her and the game’s other original character, Izis, on the game’s website.