Switch ON-sen

A Vanilla filled onsen certainly sounds like a great onsen.
...Her eyes on page 14 though. I know of heart shapes in the eyes, but a dick shape in the eyes...? I found it really interesting.
Great ending though. Heh, the old man used it with his wife many years ago eh? he seems like a really jolly fellow and I like him. 
Still, aphrodisiac was pretty obvious, but conception too? Maybe that's what made her want to have sex bareback...Intriguing.
Also you certainly have to admire his effort to come ahead of time to mess with the sign, but also manage to bring her there before someone would notice and tear down the fake sign.
The old man actually said 'again'? at the end of the sentence. So, what, many Hentai Protagonists frequently make use of this onsen and messing with the signs? If so...I'd certainly like to see them. Heck, maybe he did so too and that's how he managed to marry his wife.

she has such a lusty body, i'm in love.

Is a roofie hot spring really vanilla? I would think vanilla would have consent...

Page 9: DAT ASS!!!

'Senpai' was apparently NOT AMUSED to discover she had succumbed to the "hot spring water laced with aphrodisiac" routine.

Even as the (a-hem) "euphoria" wore off, "Kouhai" was probably thinking, even as she's 'laying the smackdown on his candy-ass' ... "TOTALLY WORTH IT!"

Im semi erected.

Conception bath you say? I demand a pregnancy sequel then!

Vanilla on a onsen! YES!

The title for this manga is 11/10.  Too good.
Guaranteed conception bath? Oh, shit. That's pretty fucking scary but also kinda thrilling.