Okay so... It's obvious someone really important to KO is gonna die. Something to make TKO come out yet again, this time for a deep and meaningful reason.

In my opinion It's going to be either Dendy or Carol. Carol is the most likely choice, as she is what one might call "The Mentor/Parental figure" to KO.

And you know what happens to a lot of mentor figures and parental figures? They die. Take Yoda, Mufasa, Bambi's mom, in fact TV Tropes has a whole trope dedicated to mentor figures dying.

Anyways, KO seems slightly dependent on his mom and whoever else might be there, and her death might trigger him to be independent and be able to defeat the final villain(Which is totally going to be Venomous, admit it).

So yeah, imo his mom's death would almost force him to mature, to be prepared to fight whatever shitstorm's coming his way.

If Dendy died, It could simply be a "False love interest" kinda story, like Yuu(That's her name right) and Sokka from Avatar.

Have them be basically best friends, and have them be closer and closer in love, and then kill the supposed lover off. Hey, Bridge To Terabithia did it.

I mean how badass would it be to see KO holding Carol/Dendy as they say their last words and breathe their last breath, then turning into a flaming rage induced TKO?