Or nobody actually did such a thing, rather Hana confessed her lesbianism and incestual interest in her sisters to Mom and the latter not only accepted it, but concocted this false story to help Hana get her first kiss from one of his sisters because neither of them is sure if any of the other girls is a lesbian, and thus this gives Hana a handy excuse in case none of them stepped forward to (falsely) claim responsibility.
According to Hana-chan's strong request...She wants the culprit to give her another passionate kiss.Oh! Oh no!I have no witness!Ah.It was me.Wait a minute?So maybe I did it when I was drunk...?I was drowning myself in booze yesterday... Kissing Hana...That's not bad, but I'd rather enjoy this as an audience...Let's stay quiet for now.To prove my alibi for last night!