Futarijime ~Osananajimi to Natsu to Imouto~

Last summer the hero of this game went on vacation and got to know a beautiful classmate of his better. Whether or not the attraction was mutual, he confessed his love to her within the short time they spent together. Now the hero is in his senior year of high school when his parent (don’t know which one) remarries and lo and behold: his new step-sister is the same girl he confessed to just a year ago--awkward. Now summer vacation has come again and our hero is considering his feelings not just for this girl, but her sister as well--despite the taboo.

[Edited from White Masq]