She called him "Raijin" enough that it's probably what he'd go by, or at least joke that maybe it's finally applicable. Hell, I'm pretty sure the final lettered version of this panel will be to the effect of
"Raijin... What have you become...?"
And depending on if she's going solo or not, I can also see her going by "Ronin" because they get romanticized in western media and DC would love playing up the edgy samurai loner bit with Tatsu.