"One day, I stumbled upon my step-sister's SNS..." A month ago, they became step-sisters due to their parents' remarriage. In search of a way to get closer to her always expressionless and cool sister, she secretly peeked at her SNS, only to find a surprising post saying, "I love my little sister!" with an unexpected display of affection…!? Caught off guard by her step-sister's gap, there are laughs and tears. A heartwarming comedy featuring a jet coaster-like tsundere sister and a pure, earnest little sister, showcasing the clumsy relationship between the two. The book is finally published, including a newly illustrated episode of the day they first met, along with the content previously posted on Twitter! 【Digital Bonus: 2 pages of newly illustrated manga】