EDIT: It was Madö King Granzört! Thanks to everybody that upvoted and contributed making the post active.

Hi! I've been trying to find this old anime that I used to watch as a kid. It was probably in the early 90s, but in could be from the late 80s.

What I vaguely remember is that, in this anime, the kids would enter what appeared to be some sort of dark room or dark space, and there they would be standing on top of a pentacle (like in the attached picture) and the moves they would do there would be forwarded to some monster or robot, so they would fight other monsters or robots.

I'm not sure if this qualifies as "mecha anime". I don't remember enough to be sure, so perhaps it didn't fit the category after all.

Any hint would be much appreciated. Thanks!