Ore ni Imouto ga Dekita Ato no Imouto no Henka ga Kochira

This is the romantic comedy that follows the collapse of my cold younger sister's tsundere personality. "I, I hate you, big brother!" My younger sister, Yukihime, is an excellent student, both academically and athletically, and intelligent and beautiful outside, but she is sloppy at home and "hates her brother." However, when my father suddenly remarried, "I can't believe I get to see her again so soon...I'm so happy," "S-senpai! Ah, um, please call me by my name!" As a result of getting two cute step-sisters who are all doting on me -- "I've stopped leaving my big brother!! My little sister loves me!!" In addition to my younger sister who doesn't want her big brother to be taken away from me, my step-sisters who are all doting from the start are also pampering me for certain reasons, and my life has changed completely! This is the result of my tsundere little sister pulling away from me. (Source: Fantasia Bunko, translated)