The Deep Sea Girl

The Deep Sea Girl (深海少女) is a Japanese manga series produced and published by Shounen Magazine R. It is a manga that tells the story of Tanaka Hikari, a girl that went missing for a whole year before mysteriously returning as a "deep sea girl" with the abilities and characteristics of certain deep-sea creatures (most notably the black swallower fish). The series primarily follows Hikari and her childhood friend Yamada as they get into crazy misadventures and shenanigans involving Hikari's newly acquired abilities, as well as the hidden world and denizens of the deep sea.

Predator

 * Hikari

Prey

 * Yamada

Scenario
After a giant squid is accidentally summoned up to the surface world, it proceeds to destroy Hikari and Yamada's school, during the chaos Hikari is grabbed by one of the squid's tentacles and Yamada, desperate to save her, reaches out to her. However at that very moment the ground underneath Yamada also breaks away and in Hikari in the heat of moment comes up with a quick idea and expands her head and mouth to inhuman proportions and proceeds to catch Yamada in her mouth before he falls. However the increase in weight causes the squid to drop Hikari, which in turn causes her to accidentally swallow Yamada whole into her stomach as she heavily lands onto the ground sporting an immensely distended belly with Yamada inside. Startled by the fact that she swallowed Yamada whole she than proceeds to quickly spit him out, and she is quite visibly upset about what she did afterwards.