Actually that character has a weird way of speaking in the anime so "desperately" is probably right for the translation.
How commendable.Somebody might come here...Mh, mh, Kakeru...U, uuuh, Rinne!Aaaaah, noo...!But this should feel incredibly good.
[Note: I know that 絶望的に literally means 'desperately', but who says that sex feels desperately good? Can someone help?]Now look at that, they're practicing eagerly.Wuoooooh! Lightning Slash!!