Kono Oneesan wa Fiction desu!?

Kono Oneesan wa Fiction desu!? summary:

Late one night when Jun was out on his bike, he came across a drunk, half-naked girl sprawled on the side of the road. She came to just enough to be uncomfortably affectionate, but Jun took her to his home to sleep it off with gentlemanly discretion. It turns out that she is Kawase Narumi, his author mother's new assistant. Unfortunately, she has no idea what she's doing in her new job, so Jun's going to have to coach her. He's also going to have to deal with her habit of getting drunk, mostly naked, and cuddly. Jun's life will never be the same! [From Baka-Updates]