this is relatively old, but it hasnt been documented yet, afaik… credits goes to javits or tinshi for the db db part of the os, but i came up with negative edge part… made in march i believe (after WCG tourney)
easy example: sagat or ryu vs rufus
downback, downback (hold), release P
if rufus doesnt do corssup, it blocks divekick (because you are in d/b), if he land in behind you, you get srk…
same principle applies to sakura crossunder, since you can block low, you either get an srk or a block. you generally want the block, so this reduces overall risk of attempting option select srk (db, df, db, df P)
this works best vs rufus because if he crosses you up, the srk would whiff, even if done properly, he must do safe divekick only to bait this. even then it is hard to properly make srk whiff if not impossible.
i think similar technique could be applied to messiah kick? this will not work with fei long dp because he has to do RDP motion…