Cat's Cradle

Prez is encouraging Riri to 'talk dirty' by offering her advice
on what to say, which suggests Riri has the ability to speak,
but doesn't because she's pathologically shy and reticent.

Here's my two cents on it: While the president is definitely a virgin, I don't think the blood found on Riri belongs to the president. This is because if you look at where the blood is on page 32, it seems to have started at Riri's clit and trickled down from there. This is important because on page 26 there is no indication that Kamitani's penis touched Riri's clit, as he immediately went into doggy style. Furthermore, at the close-up of Riri's clit on page 27, there is no blood to be found.

I think the blood was intended to be just one of those things placed for literary purposes only, so there's no need to think too hard on where it came from.