On a semi-related note, if you MUST combo after a fangrab for whatever reasons (to look flashy or something, since it adds little damage and usually in exchange for the knockdown or some tension), you can On-236S-FB Rin some characters in the corner provided that you landed On in the corner but facing away from the corner. Even then, with a 5 frame difference in startup, 236S after On can be hard to time depending on how long your combo has been up till the fangrab, but it's not quite so limited to floaty characters since 236S starts up faster.
One example of such an application: you 5S Jam from a perfect distance from the wall for a fancy combo-
5S-5H-236H-(K)hop-5K-5S-On-236S-FB Rin-walk forward a little-5K-5S-On-overdrive (optional flashiness)
If you try this combo in practice mode, you'll see that the damage after the FB Rin is scaled down to almost nothing, and you need the FB after both S and HS Fuujin for an actual post-On combo. You can always spend the 25% (or maybe even 75%) tension if you absolutely need to kill those last pixels of health though. An alternative is 236S/H-S(Nagiha) for a decent knockdown and no tension cost with some of the extra damage.
Should we strictly talk about On-236H combos with normal float height after On though, then the characters that immediately come to mind are Jam, May, and Baiken because not only are they very floaty, but their vertical hitboxes are small as well (correct me if I'm wrong on this one) which results in a longer period of staying airborne before they actually touch the ground and gain the OTG property.