Here's how this could have been done better.
After the apartment building was rendered unlivable. Kazuya would find out he can't go back home and does like he always does, lies. He tells his family he's staying with Chizuru, and tells Chizuru he's staying at a friends place.
In reality he's living in a manga cafe/cheap hotels in less than safe parts of town. One night he's assaulted, winds up in the hospital, no body knows because his wallet was stolen.
Chizuru, finally having gotten space, has time to reflect on his stupid ass and realizes that she may have feelings for him.
Meanwhile Kazuya is missing and no one seems to know where he is. His grandmother reaches out to Chizuru who realizes that he was lying to his family about staying with her. She doesn't rat him out because she either likes him or doesn't want to mess with the grandmothers illusions and also because she's a terrible person too and just likes lying.
Chizuru mobilizes all the friends to find Kazuya, who, it turns out was pretty easy to track down because his wallet was found, id intact, in the alley by the hotel he was staying at. They ask the hotel if he was there, and they find out that someone was recently taken to the hospital.
They all converge on the hospital to find Kazuya in critical condition. Chizuru, realizes her feelings, and repeats the thousand steps thing at the shrine like she did for her grandfather. This time it works, Kazuya wakes up. She confesses, they live happily ever after, lying to everyone about everything because they both suck.
Bonus: Kazuya gets beat up, everyone likes that.
Alternately: Kazuya gets hit by a car and everyone else lives better lives as a result of him having been isekai'd to the Re:Zero universe.