Warning: Spoilers ahead.
It starts by showing the call girls surprised at all the mushrooms exploding over the city. A patient of Milo’s comes by and shares the news that the Panda Clinic has been hit! Chiroru is there, meaning she got away from that fight between Pawoo and Bisco.
Rewind a bit. Milo is in the sewer with Jabi, who’s no longer unconscious. He tells Milo he only has a month to live because of the Rusting. They start talking and Jabi confirms what Milo has always suspected - that mushrooms don’t cause Rust! They actually get rid of Rust! But Mushroom Keepers and mushrooms are always in the area where rust is, so people commonly mistake those two things for causing Rust. And it doesn't help that some Mushroom Keepers are indeed evil and do things for their own selfishness.
At the same time, Bisco has an OP fight with Pawoo. Bisco tries to tell her the same thing Jabi says to Milo, but Pawoo won’t listen and won’t believe it. Bisco says he’s traveling, looking for the Rust Eater, the legendary mushroom that eats away at the deepest Rust.
Then Bisco riles her up by mentioning Milo. She believes he hurt him, so of course she won’t listen. And just wants to beat him up even more. Finally, Bisco is able to strike her with an arrow that knocks her out.
Bisco carries her back to the sewer entrance, where he’s surprised and relieved to see Jabi is alive and well. All thanks to Milo’s treatment. Bisco thanks Milo. And says he’ll do anything to repay his debt to Milo.
Then Milo reveals that Pawoo is his older sister. She’s still unconscious. They inject the mushroom stuff into her to fight the rust, and she instantly starts feeling better.
Bisco thinks it’s time for him and Jabi to escape the city and move on. But Jabi says there’s no way he can travel in his condition, so he’ll stay and hold off the pursuers. He suggests that Milo join him instead!
Bisco’s surprised, but Milo also wants to go on the journey. Because he wants to find the Rust Eater and save his sister, at all costs. Bisco warns he could lose his life, but Milo will gladly do so if it saves his beloved sister. And besides, Bisco did say he would honor any way to repay Milo.
So Bisco finally agrees. And Milo says his goodbye to his sleeping sister. He leaves his bracelet with her.
Bisco and Milo eject themselves over the gate of the city after Jabi holds off the Imihama Watch.