Should be able to reapply with your desired username with a proper email, nothing should be reserved on our end for it anymore. Let me know if it gives you any trouble though!
Happy to see your interest in aiparadise.moe! Personally I use proton mail for all my email account (https://proton.me). Can have your first and last name as your username or whatever you want, they also don't require having an email already (only if you want password recovery) hope that helps!