Of course you agree.

Even if that made you blush quite a bit too, you agree to help her wash her back, but beforehand, as you don't have as much stamina as Rei you take some time to catch your breath, while she undressed herself in the meantime, making sure that her back was facing you, while you made sure to not stare at her, even more flushed than you were about twenty seconds before. Once Rei was completely naked, she got into the water, which was deeper the further away from the shore she got, so she went far enough away from the shore for the water to go up to her shoulders before stopping, relaxing in the water while you started to undress yourself, and you understood her need to relax after the experience you had in the cavern, if Atsura wouldn't have been there, none of you would have survived for sure... But that's none of your concern anymore.

When you finally got naked, not that it took you a lot of time though, you stepped in the water too, before going over to Rei, who was still relaxing, looking at the slowly reddening sky of the late afternoon. The view had something special to it, even if it's not the first time you have a view like this, maybe it is because of the fact that you're naked in a pretty deep river with a naked vixen less than three meters away from you.

After a little while of just relaxing while watching the sky, Rei finally looked at you, with a cute little smile, saying :

"Now that we had time to calm down, shall we start washing ourselves ?"

"Well, I'm just waiting to help you wash your back." You respond with a shrug.

"I know, if you want I can wash your back when you're done with mine."

"I... Don't see why I would turn that offer down."

"Tell me, wasn't Shirayuki just a little right when she called you a pervert ?" Rei asked, with a giggle.

"Hey, it's not my fault if the only two women I stumbled upon where in this kind of situation !" You quickly reply, a blush creeping back up on your face.

"Don't worry about it, it's not like you don't like it anyway." She then says, with a mischievous smile, before walking past you, heading to a shallower part of the river, where her back would be fully exposed, before wagging her tail while waiting for you to come over, which you eventually do. After you got closer to her in her back, she uses her tail to put a small brick of soap in your hand. "You'll need something to wash my back, after all." She then says while you stare at the brick of soap for a second, wondering where you've seen that before, because you were sure you've seen that before.

After eventually dumping this question, you get even closer to Rei's back, and since it was already wet, you started softly rubbing the soap brick on her back, to make it all soapy, before giving it back to her by just putting it on her shoulder, and lucky her, she had the reflex to grab it before it slid down into the water. After she stopped moving again, not washing herself at all for some reason, you start slowly rubbing her back.

It felt cold, but incredibly soft under your hands, and slippery if that wasn't obvious enough with the soap on her back. You couldn't help but just like the feeling of her soft skin against your hands, as you rubbed it clean with soap, slowly and tenderly, rubbing her sides too, from her lower back to her shoulders. Meanwhile, Rei quietly whimpered at the feeling of your hands on her back. Her last heat period had been so brutal that she was still quite sensitive as it seems, but you don't even notice her whimpers, absorbed by the task you had, and wanting to do it as best as possible.

But every good things comes to an end at some point, so you eventually finish rubbing her back, before sinking your hands into the water to start rubbing it once again, this time rubbing off the soap. Was this an excuse to feel her back some more ? Absolutely, and this time, you could clearly hear some of her whimpering, which aroused you quite a bit, as you started to feel the blood rush into your dick.

When you finally finished washing her back, you took a step back, to calm yourself down a bit, but Rei, without even turning around, wrapped her tail around your waist before pulling you against her back, your dick pushing between her ass cheeks, something that she clearly felt, as she moaned slowly, before taking your arms (after two tries, because it's not that easy to grab someone's arms when they are in your back) and pulling them around her slender frame to put them on her belly, saying right after, as if she could see your blush :

"You're not done yet, are you ? Because the work is only half done, dear pervert."

You didn't even bother answering, as you were flushed and stunned by her bold act.

(I'm starting to think about making a discord server, or something like that, to chat with you, to get your possible suggestions, to update on some things, and more. Is it a good idea ? You can tell me by commenting, and if you were wondering, it'll be free for sure, because why not after all ?)