Osushi is a merchant who used to be far better off, but her parents died and her brother Tanousuke went off to fight for his lord. She’s prayed for his safe return every day since…for five years. Dororo, not exactly master of tact, tells her that’s…pretty long.
But Dororo is also a master of reading people, and he can immediately tell she came from money despite her tattered clothes. Osushi’s prayers are answered, but the brother who left her to uphold his honor and loyalty is not the same man anymore.
When Hyakkimaru, standing in the rain, “listening” to the drops fall, rushes towards the red sword he sees in the distance, he and Dororo find an entire convoy of people slaughtered. The swordsman tells them his blade thirsts for blood, always.
To Hyakkimaru, it’s just another demon, even if it’s using a human as its instrument. He makes good use of his prostheses by taking having his fake leg run through then tossing it aside, separating it from the man. But when Dororo runs to retrieve the leg (as he always does) and touches the sword, he becomes its new servant.
Like the One Ring, the sword bends its holder to its own twisted will, putting Dororo in a trance when he tries to resist. Back in the village, Osushi has retrieve the sword’s original holder, who turns out to be her brother Tanousuke. While initially elated by his return, he was accompanied by so much blood and death and won’t speak to her, so she knows something’s not right.
Filling out the broad strokes of the cold open, we see Tanousuke’s lord order him to use a dull, rusty sword he’d pulled out of storage to behead a captive. But with each captive he kills, the sword, called Nihiru grows sharper…and thirstier. Eventually Tanousuke turns the blade on his lord (serves the lord right, really) and massacres the entire camp.
Needless to say, if there’s any part of Tanousuke left, that part probably laments still being alive and being used only to quench Nihiru’s thirst. But the part of him the sword twisted into its service only wants Nihiru to return to him, hence his utter ignoring of Osushi’s tearful pleas to stay with her.
Nihiru has Dororo bring the sword to Nihiru, but is intercepted by Hyakkimaru. For a moment, Dororo isn’t sure Hyakkimaru knows he’s not a foe, and attempts to dodge his strikes, but there’s no doubt who’s the superior warrior. Thankfully, Hyakkimaru merely knocks the sword out of Dororo’s hand without harming him.
Unfortunately, Tanousuke is there to pick Nihiru back up, but the sword has taken its toll on his body and mind, and he can’t quite keep up with Hyakkimaru, who kills Tanousuke and breaks Nihiru’s blade. Her brother’s imminently peaceful expression upon dying, as if he’d finally been released from an extended stay in hell, is little consolation for poor Osuhi, who is alone once more.
Nihiru, being one of the demons in the Hall of Hell with which Daigo made a deal, releases another part of Hyakkimaru upon its defeat: his real ears and sense of hearing. The first things he hears in his life are the steady falling of rain and Osushi’s weeping.
Meanwhile, back in the Hall of Hell, Daigo is now aware that someone out there is killing off the demons he made a deal with. Even if the demons haven’t double-crossed him yet (why would they uphold their end of the deal once they got his son’s parts? They’re demons), the good fortune he’s enjoyed is unlikely to last if Hyakkimaru continues knocking them off.