True; OTOH it really does have a girl jonesing for her sister, so at least it's in "definitely incestuous feelings" territory, even if nothing's really happened.
Of other titles... Blue Monday is first cousins, meh.
If you filter out the explosion of stuff by Taiyaki, I think the next really incestuous stuff is Tae-chan 38 in Nov 2025, with mother/daughter stuff via threesome.