The mall had a (most likely gas) explosion, and there are many dead being found inside https://newsdig.tbs.co.jp/articles/-/2833412?display=1

For the record, Aeon Mall is basically a brand - there are many Aeon malls in Japan in various cities.

The second floor of the mall exploded for some reason, and the roof collapse is secondary to that. It seems to have happened after the earthquake and subsequent evacuation. There are videos of people leaving the mall:

https://x.com/yuto4388/status/2082060992377475247/video/1?s=...

That mall was also damaged in a similar earthquake that happened in 2016.