Veza
Veza, or The Tower, is the one setting the Heros on their path, and supporting the protagonists. She is working with the Heros, and while she has an agenda, her agenda is (initially) the Heros' agenda.
What She Wants
It's perhaps easier to define what Veza doesn't want. She doesn't want to face Umumtu right now, feeling like she's the reason the world is broken. She doesn't want the world to be broken. She doesn't want to feel like she can't talk to Umumtu, or like she can't ask for Umumtu to forgive her.
And, most telling, she doesn't want Umumtu to be the one to fix this.
The Plan
The key is the Kivuli. Veza has managed to get a few under her control, and is now attempting to experiment on them and learn more. Meanwhile, Umumtu's corrupting humans; that needs to be stopped, and the last time the Heros worked well enough, that's what she's going to go with again this time.
But, in the end, she needs a Kivuli and a Human to have a child together. That will fix everything. Probably.
Immediate Steps
The first step is to create a dangerous situation, and force the two groups to work together. Thankfully, Umumtu's made this easy; she needs to be stopped, the situations she's casting a light on should probably be resolved, and it adds enough danger for the Assistants and Heros to work together.
Intermediate Steps
As feelings inevitable develop, encourage them. Put one of the objects of affection in harm's way, and let the other sacrifive (non-fatally) for the other. Build a strong bond of love, meanwhile forbidding it. This will force them to choose each other over the world, and if they manage to do that, there's a strong choice they will be able to weather anything.
Long Term Steps
The child is key. They must produce viable offsprint. If the world was ended with a kiss between two, before, a child should fix everything.
Because a child is the end goal, focus will have to be places on male/female pairings.