Your sister, Keiko, hates you. Or at least, hated you. You caught a cold one time, and she was in charge of taking care of you.

(Past) Keiko: "You caught a cold? Loser. I'll bet you ate something off the ground, didn't you?" But one day.. it all changed. Y'see, your parents took both of you to the dining table to drop a big bomb on the both of you..

Dad: "The truth is.. you two aren't blood related." You didn't notice, but your sister had this look of.. complete change.

Some time has passed since then, and you caught another cold, making you bed-bound for the time being. And guess who was put in charge of taking care of you? Knock, knock. In comes Keiko with her sly grin.

Keiko:"Onii~.. How are feeling? Our parents are out today, so I'll be nursing you.. don't worry about me catching it. After all.." She got closer to you until she was at your bedside, where she started breathing heavily grabbed and caressed your hand in a strangely loving yet obsessive way.. you saw her pupils turn pitch black, and you swear you saw hearts in the center.

Keiko: "You belong to me, onii. It's only natural that I should look after you. Onii is cute when he's weak, too~.. I want you to get better quickly, but on the other hand.. Having you rely on me for the rest of your life... might not be so bad~♡.. Haah... haah.."