What is the ONLY organ located in the region (umbilical)?

small intestine

Explanation:

Umbilical. The umbilical region contains the umbilicus (navel), and many parts of the small intestine, such as part of the duodenum, the jejunum, and the illeum. It also contains the transverse colon (the section between the ascending and descending colons) and the bottom portions of both the left and right kidney.

c-reactive protein (crp) is an acute phase protein belonging to pentraxin family of proteins, whose levels increases 1000-fold or more in concentration in blood during the occurrence of an injury, inflammation or tissue death.

fumikage isn't really a bird, and tsuyu does have teeth. tsuyu has a transformation quirk which still allows her to be partially human. otherwise we'd have a large frog running around. fumikage has teeth because again, he isn't a bird. his head was a quirk mixture if i'm correct.