After 4227 SRs, shiny Latios appeared in my Japanese Black 2! It is my fastest shiny charm hunt to date, even though it went over the shiny charm odds, like the rest of my shinies I caught with said charm(it's a lie ).
The battle was quite long, with it fainting my Watchog, but I used a Max Revive, and stalled using Zorua. I managed to catch him in a Dive Ball like I wanted to. My Modest synch Espeon worked and Latios is Modest!
I have no idea what I'm hunting next, but it will be a RE shiny instead of a SR one.