Once the Big Shuffle is done with, Shinji lathers up his own hands in preparation for returning the favor.

His own movements as he reaches up to give Kai's shoulders an initial rub are probably a little more deliberate than would really be conducive to the 'quick' aspect of this shower, like he's particularly concerned with getting this 'right' or perhaps just being thorough, that speed is left an afterthought.

Definitely, though, this way around feels a little less inherently stressful. Like this degree of control over this situation makes it that much easier. This would be a lot easier for him to get used to.

Time for you to get nice and clean, friend!