@Shinobu "S" or "SS" are the ranking the mafia gives to kids that are/have been abducted. Great and the gang are all "S" rank kids
@Scrabbleman I think you both are talking about the kid that killed the mafia guy and that was holding a gun, From what I get, he/she is a new character we've never seen
I’m gonna assume Gerbain probably gets killed by Great going into red eye mode. If not Gerbain would be so op as an adult if this is how strong she is as a child.
After looking at past chapters: @tprat is probably right in that the SS kid is probably Kiriya.
The right age in the past/present, same hair, same eye color, using guns, past connection to Great, Great in the present time implying present Kiriya holds back a lot and that he lets some criminals live instead of killing them(easy to see where he got that from), ect.
It would actually be odder if SS-Kid isnt little Kiriya.