This is one of the... ahem, quintessential doujin cohabitation games. Quite a few of them on a certain website follow its formula to a tee.

Why? Because it just works.

You play as Onii-chan, the elder brother of the little sister you dote on. Sickly and frail as she is, you are tasked to take care of her. Part and parcel for such kinds of games, if you have certain patches installed, which you should, you'll be doing more than just taking care of her.

Unfortunately, for the sensitive or those who have been affected by it, this does have contents of SA, of the sleeping kind. Your options are rather varied and there are multiple positions for you, but the game deliberately uses no Live2d, to match with its manga aesthetic.

This is not a game for the prudish nor for the morally-inclined.

Beyond that, there's a surprising amount of activities to do with a basic plot involving you trying to save your guild and an adventure subplot where you go with your sister to distant places to seek a more-permanent solution to her predicament.

It's not too fast, nor is it too slow, but if your... festering needs requires buildups and you're fine with the beautiful Manga aesthetic, this can suitably help with your... requirements.

Note the Official English version, while having some slightly questionable translations (what even is Blow on?), has a better sentence flow which actually makes the thing worth reading this time around.