Remember the carrot meme? It's a joke on the surface, but it's all the evidence you need. Chizuru has already "rejected" Kazuya in those 3 months, but instead of moving on, her feelings for him grew stronger. Then that push from Mini equalized their roles in the story. It made her realize she can't get over this guy unless she faces him head on.

Now Chizuru's been doing 95% of the chasing. Also since this was hinted by Mini, this should also be clear: she's not "investigating" anything. It's a sham, she's just testing the waters with him. She likes him and is easing herself into a relationship by finding ways to hang out with him alone. That's her "investigating". Even that earthquake incident was a poor attempt by her at flirting by finding an excuse to touch his hair.

You should be a lot more worried about Kazuya, who has managed to (miraculously) misinterpret every single situation involving them in the new arc, and is somehow convinced she's hooking up with another guy.