As far as I’m aware, “Nee-san” can mean both sister and older sister, while “Onee-san” specifically means older sister
Therefore “Nee-san” and “Imouto” are interchangeable here
Wait it's ended?
Similar vibe ending to Kiraboshi Ojou-sama no Kyuukon, tbh.
Maybe a little more conclusive though.
Thank you for the SLs Boku Alliance!