Fire Force and Soul Eater have a very serious connection. Creator of both, Atsushi Ohkubo, confirmed with the final chapter of the Fire Force manga that it’s actually the prequel to Soul Eater.

At the end of Fire Force, its main character, Shinra Kusakabe, is seen overlooking an area of his own creation. Turns out that this is where the majority of Soul Eater takes place.

Source: https://www.distractify.com/p/is-fire-force-connected-to-soul-eater