Minikko Half ~Naisho no Ano ne~

The protagonist Takejou Subaru lives a usual boring life, but one day he is offered a part-time job of the private tutor by his first love, who has just returned from the USA. His students are her daughters, half-blood twin sisters: Maria and Alice. "A-ah, ni-nice to meet you" - those words spoken in basic Japanese, emerald eyes, and... blond hair! Those girls suddenly appeared before the hero's eyes just like perfect angels. Or so it looked like... Maria-chan has an unexpected weakness: she is extremely sensitive to any touch. She becomes excited even by the slightest touch of a man. And now she's living under the same roof with one. While doing his job as a tutor, the hero is ready to take care of her body and soul! [Translated from Official site]