The "Red Herring" was when Oba Koko's nephew, Kiru, set fire to her teahouse. This made me think that Kiru set all the fires in Edo, but he didn't. Another reason why I thought he set the fires is because he also did another criminal act: he stole Seikei's teahouse clothes and wore them while he set the fire, so he framed Seikei, and Seikei got in trouble!