A Weak Nobody, But I Can Eat [Sentinel and Guide]

In the year 3316 of the Star Calendar, a pollution source had infected most of the interstellar realm. At the same time, several major star systems joined forces to raise a shield, protecting the last sanctuary. A chaotic junk planet that had been half-infected before the spread was halted was being livestreamed by StarNet media in all its misery. "Behind me is a junk planet at the edge of the shield. Half of it has become a polluted zone, and before long, the entire planet will be infected. The residents can't leave because they're poor, so all they can do is wait for aid..." As the reporter spoke, a spherical camera flew into the polluted zone to livestream its depths. The houses had turned a lifeless gray. Many people risked their lives searching through the polluted area, their clothes filthy and tattered. Only one person stood with her back to everyone, making a crunching sound. Two mutated devil spores had sprouted at her feet. Once infected by these spores, even an S-rank Sentinel couldn't escape them. The comments flooded with panic: "Run!" "Once those spores split open, everyone in this polluted zone will die!" "That kid, is she a girl or a boy? She's definitely going to be the first to die. May God protect her." Just as the reporter called through a loudspeaker for people in the polluted zone to get out, a series of crunching bites sounded. A palm-sized little blue fish suddenly swam out from in front of the girl. Under everyone's horrified gaze, it took two quick bites and swallowed the spores, chewing away. Comments: ??? Comments: !!! The reporter was stunned and asked, "May I ask which Federation Super S-rank Sentinel you are?" Rong Yu: "Chew, chew, chew." The reporter asked, "Did you come specifically to rescue the junk planet?" Rong Yu: "Chew, chew, chew." Getting no answer, the reporter said, "I understand. You must be here on an important mission! Your Excellency, esteemed Super S-rank Sentinel!" Rong Yu stared through tears as her spirit entity chewed away: "..." Your Excellency, Super S-rank Sentinel? She's only a D-rank Sentinel, okay! * Rong Yu transmigrated into an interstellar world and awakened as a very odd Sentinel. Other people's Sentinels had lions, wolves, tigers, and leopards. Her spirit entity was a palm-sized little blue fish, too small to even make fish soup with. Other people's Sentinels had spirit entities that didn't need to eat. Her spirit entity not only needed food, it would only eat mutants. Rong Yu: "Just eat, what else can we do?" Could it really eat all the mutants? By the time most of the interstellar polluted zones had been eaten away, the little fish had grown into a big fish... Rong Yu stared blankly, then fell silent. "Well, since things have come to this, let's eat first." * The interstellar realm entered a great new era, and humanity finally defeated the ever-stronger mutants. And the reason was... Well, a fish had nearly eaten them all into extinction. :) Note: My take on an interstellar Sentinel/Guide setting, with plenty of original worldbuilding. BG, not GB. Female Sentinel, male Guide. The pairing is a little cat: more than a background character, a comrade-in-arms and lover. Theme: Keep living your best life.