TL note: on page 3, Yuu uses the term 義妹 (Gimai) which means a younger sister-in-law, hence why she says the side comment “Even though she is older than me…”.
Well, seems obvious that the fmc's big brother's love interest is gonna be mc's big sister, so brother and sister are going to date each others' brother and sister, the family trees will be very tightly entangled
So... Between her being the one nii-san is interested in, and her being the one he's interested in... What are the odds that she's the one Tsuruse's nii-san is interested in? 🤭