Hmm maybe he wanted to create a reason as to why he wanted to break up with the sister, and then suddenly disappear. However, he didnt expect kusakabe to visit his place or for the sister to call his workplace (both verifying he had a fake identity the whole time). But then again, hes a con man, so I dont think he would let all if that happen. Maybe we will see
Or it could just be the simple explanation of: he’s crazy and he just wanted to toy around with kusakabe for a night before ditching his identity
that sounds like a likely explanation but she would have known he scammed her out of his money since she and him are the only ones with access to it right? so then the breakup excuse would only distract for a moment until he took the money and ran and also, it would only be an excuse for kusakabe as to why his sister and scammer broke up since i doubt the he told the sister he slept with her brother causing him to want to break up? but maybe he did tell her and we will find out in the next chapter or maybe like you said he just wanted to have fun and is crazy
like what was even the point of pretending to sleep with kusakabe when he was going to break up with and steal from his sister either way? did he also steal from kusakabe while he was knocked out? he could have stolen from kusakabe without pretending they slept together because either way kusakabe kncked out from drinking or getting drugged. why they whole pretend drunk hookup when the sister never found out they "hooked up" so its not like it caused a divide between the siblings?
lol just want to understand how certain decision this asshole made even ended up helping his robbery? the fake engagement makes sense and stealing from a drunk kusakabe makes sense but how does pretending to hook up even help at all