Cobalt Plus: Kagerou 3 (Patreon)

The underground waterway was extremely narrow at some places - it can pass along water just fine, why would a human ever try to go through it?

Female ninjas maintain a slim torso through laborious exercise and highly restrictive diet; and they can dislocate their shoulders if they need to squeeze through. But this opening was exceptionally small. 

Requester: https://www.patreon.com/user?u=2801550