Episode 124
"How do YOU know?"
Rin dropped Anotsu's name as Dowa was just getting ready to slice-and-dice some eta-nin wearing Isaku's armguards.
Rin tells her a little about her past... or at least hints at it. She tells Dowa that she's been involved with Itto-ryu (but not to what extent), and that she knew it from the time they met Kashin Koji... but suspected it the first time she watched Dowa's incredible fighting style.
After talking for a minute, Dowa calms down, and at that point the poor eta-nin is on his knees, praying for forgiveness, and offering the armguards and an explanation- He tells them that he didn't take them off a dead guy, but rather got them about 10 days ago as a gift from a guard in the "Mamiana". He tells them the location of the mysterious "Mamiana", a cavern on the side of the mountain.
. 
They were told that people come out about 2-3 times a day. Dowa gets ready to go in there and fight, but Rin (again) stops her, telling her that it's suicide- Rin's figured out that this tunnel connects to Edo castle (and that they're covering up this mass of bodies by not taking them out the regular exits). You Dont. Attack. Edo. Castle.
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