I'm reading this one as slightly more complicated than others seem to be. The setup seems to be that Kana is trying, with decreasing levels of subtlety, to seduce her little sister ("Whoops, you overheard me masturbating!" "Here, sis, have an assortment of sex toys!"), while Hana is crushing on Touri, with about the same scale of blatancy. Meanwhile, Touri is seriously checking out Kana as soon as they meet — hence the triangle, which Kana then proceeds to collapse. But Hana seems pretty used to masturbating at her sister's noises, so I'm kind of onboard for the implied eventual threesome.
That said, I'm a little annoyed by the violation of the old storytelling principle of Chekhov's Dildo: if there's a sex toy in the first act, somebody should be getting off on it by the third act