I use Chun/Asuka.
The biggest problem Asuka has is against zoners and good footsie characters. Chun is there to counter act that and provide a good hit confirm for Asuka. If Chun lands a s.MP xx Legs, it’s easily hit confirmable to a Tag Cancel to Asuka starting a combo with s.HK if you’re early enough, leading to 422 damage from a simple s.MP with Chun. The Tag Cancel requires one bar initially, but Chun can lame it out for that first initial bar and the best part about this combo is that after you spend meter for that first tag cancel, you build half of that lost meter back in the process.
Chun and Asuka can also easily loop together pretty well even though I’m sure other characters can use the same loop for more damage, so try experimenting. For example…
(Chun) c.LK c.LP [b.MK > MK] Jump Cancel, j.HK, Land, cs.HK, Jump Cancel, Stomps x3, Tag Cancel, (Asuka) f.LK f.LP c.MP Onikubigari, Tag Cancel (Chun) cs.HK, Stomps x3 Tag Cancel… keep looping for as much meter you have for cancels.
(Asuka) j.HP s.HK xx Upkicks j.HK s.HK xx Onikubigari, Tag Cancel (Chun) cs.HK Jump Cancel, Stomps x3, Tag Cancel (Asuka) f.LK f.LP c.MP Onikubigari Tag Cancel… etc.
Gems wise, Chun/Asuka both have life regen, some sort of meter building gem, and speed gems. The meter building is SUPER important for Asuka since she’s a pretty big meter hog and needs that meter desperately in certain matchups (coughcoughGUILEcoughcough).