Invertigo

During Shadow's covert mission on halting a sabotage plot whilst searching for Sonic's whereabouts onboard the luxury liner -- R.M.S. Alexandria -- she is capsized by a massive anomalous rogue wave. The mission abruptly switches from a counter-sabotage op to a fight for survival alongside with other passengers to reach from the upper decks to the ship's hull, the only area above water. It's only a matter of time until the Alexandria slips beneath the waves, although a threat still loomed above the rising waters inside the inverted bowels.

(Part of the Sonic Borders AU, an alternative universe created by me.)