It's lethal/fatal/mortal. Personally, I like "fatal" the most. It sounds like "fatality" from MK.
As for Gin? Better to hope (if one must) that Askin isn't the Sternritter version of Gin.
Eh, doubt it. Gerard's epithet hasn't been demonstrated and I could see Askin being saved for last.
I have to agree here.
Askin's schrift and your translation of the kanji tell me that his ability will be key to overthrowing the Soul King.
It would certainly make for some hilarious irony with him looking so much like Aizen in appearance.