From the outside, Taesung and Haeun look just like real siblings. They were certainly raised that way, living together in the same house since they were kids. But here’s the secret: they aren’t actually related. Haeun’s just been living with Taesung’s family since her parents went to live abroad, and that’s the way it’s been for the last 15 years. They’re basically real sister and brother at this point…until one day, Taesung comes to learn a prank from his friends. Grab a girl’s sides, and you can tell from her reaction what she really thinks of you. Taesung tries this out on Haeun that night, eager to see how she reacts…and accidentally ends up grabbing her boobs. Uh-oh. But just what is up with Haeun’s reaction? She’s blushing, squirming, not saying anything… Is this how you would normally act in front of your brother? Things come to light, and Taesung’s starting to look at his “sister” a little bit differently now…

Original Webtoon:
R19: Lezhin, Onestory, Nate
R15: Naver Series, Ridibooks, Bomtoon, MrBlue

Official Translations:
English: LezhinUS, LezhinX, Toomics
Others: Thai*, T.Chinese, French, Japanese, S.Chinese, T.Chinese, Spanish (LA), Italian, Spanish (ES), B.Portuguese

The Thai translation merge the prequel and its sequel into one site.