Flandre

Feet are one of the most disgusting part of the body, they are covered in grime and stuff whatever you do as you walk on them and even shoes and socks will make them dirty and sweaty as well. Probably the only time they are okay is just after a bath or something.

Seeing she probably never used them and even if she did it wouldn't matter due to Hourai Elixir, I would say that Kaguya objectively has the softest feet of all 2hus