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 interacting with 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 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 sudden increase in size and 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 with a ground-cracking force, Hikari is visibly shown now sporting an immensely large and distended belly, with Yamada shouting and struggling inside her stomach. Startled by the fact that she swallowed Yamada whole, Hikari than proceeds to quickly spit him out. Afterwards towards the end of the chapter, she is shown to be quite visibly upset about what she did to Yamada.