Originally Posted by
Asetotti
Hikari is Touka's mom, now confirmed to be Yomo's sister (the guy who trained Kaneki and Touka very early in the manga and also took Touka to safety when shit hit the fan with Anteiku. Also Uta's friend.)
Narukami is the name of Arima's "thunder" quinque. Literally the name means "The god of thunder" and hence the chapter "Thunder rabbit". The timing of the flashback and the name of the chapter heavily imply that Narukami might be Hikari, Touka's mother and Yomo's sister..
IXA is the name of Arima's other quinque which broke when Arima fought Kaneki in the original manga.