Somehow two lines of lyrics from a well-known rock song popped into my head as I read this - what follows is a spur-of-the-moment re-write to match (hopefully) the opening of this story:
"Then they stood in the doorway, for what I couldn't tell. And when I learned the reason why, then I was caught between heaven and hell."
But seriously, a choice between "Cool & Sexy Onee-san" and "Tsundere Imouto" ... that would be (pardon the term) a HARD CHOICE for any healthy young man to make. Do Your Best, male protag-kun ... you Lucky Bastard (GRR)!
P.S.: anyone who responds to this comment by making reference to 'Emilia' will be shot - figuratively, of course.
This was great and definitely had some hot scenes.
In terms of the choice, i mean I would always want the harem end lol but if i really HAD to choose, the older sister definitely wins. All the younger one has on her is being a tsundere and thats rarely a win for me lol. The older sister's body, expressions, and scenes were definitely hotter.
I'm assuming that when they use the term"first grader" the actual translation is supposed to be"first year" which usually refers to freshmen from high schools and universities