The story seems to be something quite overused in many yaoi anime (or even normal guygirl romace. Or even Yuri.): "OMG I'm in love with this person but I've never seen him but owh my gawd he was just under my nose all this time!!!" I mean it's like, "Give me a freaking break. Another one?" And then you'd just walk away and roll your eyes. And even the conflicts are way too commonplace- "oh my gosh i can't accept you because you're my son's bestfriend" and the whole "my-family-won't-accept-you-so-do-I-break-up-with-you-or-not" kind of thing. Absolutely nothing can catch your eye, and all ideas are overused. Even sex scenes aren't all that hot. Even the sex scenes in Haru wo Daiteita OVA are better.
Even the characters are not that great. We have the typical (and by typical I MEAN typical) uke who's beautiful and cute and wimpy and short-tempered but can't resist the seme, and a seme who's serious, TDH (tall, dark and handsome), and quiet. I mean, I can mention a pair off the top of my head who's like this: Kazahaya and Rikuo from Gohou Drug. Owh wait, there's Tsuzuki and Muraki too from Yami no Matsuei.
Basically, it's just something you pull off the shelf of mediocre cliches. If you're looking for something fresh- skip this and look for something else. Like Haru wo Daiteita.
One thing I can commend though is the art. I haven't seen such elegant art in a long time. Although really~ it's kind of unrealistic. I mean, the grandfather looks like he freaking took a bath at the fountain of youth AND drank the water. I mean, it's just unrealistic. And the eyes are kind of weird- but if I guess you're looking for fresh anime eye art, you can look at this one for reference.
Overall, the anime is something not worth wasting your time on. Although, if you don't too much mind the lack of plot (or the mediocrity of plot anyway) or the lack of hot sex scenes, then watch this just for pure entertainment. Like I dunno, when you have nothing else better to do with your life because you've seen every yaoi anime out there.
And really, don't even bother watching this when you DO have time to waste. If you DO have time to waste, go watch the Haru wo Daiteita OVA or something. It's not good either, but at least it's better than this one. Anything is better than this one.
So pass this and go for something else instead.
Owh and by the way, if you were expecting incest because of the title (Like maybe you read Papa to Kiss in the Dark and want something of the same nature), well sorry to burst your bubble but it ain't incest. It's shota, but not incest. (Kirepapa means beautiful papa or something, apparently a combination of the words kirei= pretty and papa= father. I dunno, I'm going from memory here).
