Starting off from scratch.
What can you do on what space with Ibuki vs. - lets see… Ryu, good example. You mentioned it.
I just picked up Ibuki coming from Chun, having a good understanding of footsies in general and I know how it feels to “play under pressure” with no get-ouf-of-jail-Freecard. Without a knockdown or confusion in the air, I play my Chun-Game.
I can’t do fancy SJC Combos, I keep my mixups to a minimum, I got some unblockables, Safejumps and Option Selects in my reportoire.
First rule. Do not let them jump-in for free. b.MP into Knockdown or Air-Throw is your best friend.
Second rule. You don’t have to initiate the fight. We have no fireballs, so what? Land one slide (maybe into knockdown?), have life lead, let them do something stupid. Be patient. Control your space!
Third rule. Have a good defense. Tech throws accordingly, block and punish to return momentum, make use of EX Kazegiri if you feel like you have read a pattern.
Up close, you have momentum. Ryu has 2 bars? Expect a reversal DP, just block and wait between your frame traps (s.LP, s.MK, stuff).
Whiffpunish with cr.MP into Neckbreaker (hard to do against c.MK, but stops forward momentum)
You got meter? EX Neckbreaker the shit out of his fireballs.
Got no meter? Space your slide well.
Knockdown? Pry him open!
Stop the gimmicky stuff. You can apply command dashes to complete your stun or open up the defense after knockdowns (e.g. b.MP, HK CD, HK Kazegiri Knockdown -> MK or HK Command Dash to get offensive going.)