Also known as: ぱふぱふ, かまくらぱふぱふ, 头夹在胸部之间
When a character's head is between someone else's Breasts, especially when it's all the way between.
See Face Between Breasts, Face To Breasts, or Breast Smother when they're face first. See Breast Pillow or Head On Chest when the head is simply resting on top of the breasts.
The male equivalent is Head Between Pecs.