In case anyone's interested: The whole "hug ritual" thing has a scientific basis. Physical affection (positive physical contact in general) causes a release of oxytocin. Oxytocin is one of the main factors in the phenomenon known as "love", but it also plays a role in social bonding and such. It's essentially the "affection hormone".
Note: It also plays important roles in the reproductive systems of both sexes, as well as child rearing. Not that this is relevant to the story, but I want to emphasize the significance of oxytocin in human development. A lack of oxytocin is part of why babies that don't receive enough physical contact are more likely to die, as well as why some people experience the phenomenon known as being "touch starved". Sherryl is essentially making Akira a little more human with each of her hug sessions. And heck, it helps her too. I don't imagine there are many she'd trust to hug like that (the affection building is probably even stronger with her, realistically speaking).