Yes, Before the Coffee Gets Cold by Toshikazu Kawaguchi is a clean book.

In a small Tokyo café, customers can travel back in time — but only for as long as it takes their coffee to go cold, and only if they follow the café's strict rules. Toshikazu Kawaguchi's gentle time-slip novel is more about regret and reconciliation than science fiction; warm, wistful, and entirely wholesome.