Eien to Natta Rusuban ~Papa wa Kaeranai~

It has been two months since Kazama Kazutoshi began his service as a PE teacher at Reigatake Academy. He had lost his wife half a year ago due to an accident and kept raising his single daughter by himself. One day, Kazutoshi's grandfather gets into an accident that leaves his body heavily bruised and he becomes unable to move. Kazutoshi is about to take his grandfather into his own custody, but is met with stubborn resistance. Kazutoshi has no choice but to nurse his injured grandfather until he can move by himself again. His daughter also recognizes the necessity. However, his daughter finally was able to find some friends at her school and doesn't want to be separated from the life she had built up until now, which leaves Kazutoshi with a dilemma. Not to mention that he neither has friends, nor co-workers nor close relatives he can contact about this. The situation makes him lament his difficulties to socialize with others. But at that time... -in an unexpected turn of events- he encounters a doctor named Ogata Seishirou. After hitting some booze with him, Kazutoshi comes to the conclusion that "This guy can be trusted" and implores whether he could care about his daughter for a short while during which he is absent. Ogata turns out to be the managing body of the school Kazutoshi works at, contributes to supporting him financially and moves out of his current housing and to proceed to rent an apartment right next to Kazutoshi's. All these gestures make Kazutoshi largely grateful. But... there is something that Kazutoshi didn't notice about Ogata. Ogata Seishirou is one of the world's most heinous individuals - and the protagonist of this story as well. And that is how Kotoko's eternal housesitting begins... [Translated from DLsite]