WARNING: The following contains spoilers for Rust-Eater Bisco Season 1, Episode 7, "The Stolen Rust-Eater," now streaming on Crunchyroll and Funimation.
Episode 7 of Rust-Eater Bisco may not have taken its opening battle to epic heights, but it did reveal a huge secret that greatly increased the stakes. Bisco and Milo have finally found the legendary Rust-Eater, but the key to its success in ending the Rusting lies in an unexpected place -- a Mushroom Keeper's blood. This new development takes a page from Demon Slayer, where retrieving samples of Muzan Kibutsuji's blood is integral to Tanjiro's quest to save Nezuko, and may even be the key to understanding how to defeat Muzan himself.
Bisco and Milo's initial excitement at finding the Rust-Eater quickly turns to disappointment when Bisco reveals they may well be ordinary mushrooms, given their taste. However, Milo notices something important; while the Rust-Eater tasted ordinary, once it came in contact with the blood on Milo's hand -- Bisco's blood -- the mushroom suddenly began to glow. While it wasn't made clear what that glow entailed, it was clear that somehow, Bisco's blood was the reason the mushroom began to "work".
Bisco is immediately baffled by this new discovery, wondering why Jabi would have kept it hidden. Milo alludes that maybe it was to protect Bisco, and perhaps all other Mushroom Keepers. Rust-Eater Bisco has already mentioned more than once how not all Mushroom Keepers are necessarily good, so there may be in-fighting if this secret were more widely known. However, it's also not a far leap to assume that such information could easily be weaponized and aid in the further eradication of Mushroom Keepers were it to fall into Governor Kurokawa's hands.
The threat of the Governor returned in Episode 7, rendering Bisco and Milo's somewhat triumphant turnout into another huge setback. Kurokawa ends up taking the dead pipe-snake and, while Pawoo won't be able to do much without the key knowledge they just attained, it's not as if any of the three were able to secure significant samples of the Rust-Eater. Even with what Milo could save, the mystery now lies in discovering how and why Mushroom Keeper blood is necessary to begin with.
Another hitch in the plan appears after Kurokawa shoots Bisco with a rust bullet during their brief fight. Bisco plays it off, but Milo knows the severity of the injury, noting that this infection has a higher potency and will spread faster, rivaling those of even Pawoo and Jabi. Milo fights tooth and nail to give Bisco treatment, and it remains to be seen whether or not this will affect the efficacy of Bisco's blood.
Kurokawa's appearance also begs the question: did he get the information about the pipe-snake from Jabi, or has he been in the process of capturing pipe-snakes all this time? Either way, his actions prove perilous to Bisco and Milo's plans, their safety and now Pawoo's. Pawoo leaves the others so they can find more of the Rust-Eater, while she tries to gather more intel on Kurokawa's plans.
She also leaves to save Jabi, with Milo giving her two newly synthesized doses of Bisco's blood and the Rust-Eater, one for Jabi and one for her. Milo may think he's the closest he's ever gotten to saving his sister, but Pawoo secretly foils his plan when she gives her dose to Bisco just before she leaves. Her reasoning makes sense -- Kurokawa would stop at nothing to discover how she got rid of her Rusting so quickly -- but Rust-Eater Bisco fans can only wonder what rift might be created if Milo finds out.
The tension continues to thicken when, upon arrival, Pawoo discovers that Kurokawa has turned her unit against her. She also sees Jabi's been taken hostage, making their fates all the more intertwined. When Kurokawa uses the emergency alert system to call for Bisco and Milo's capture, their plans and trust in each other quickly crumble. With such an emotional end to Episode 7, Episode 8 could easily shape up to be another doozy.
