Common Interests of Humanity
When Ves heard how hard it was to integrate different resonating exotics into a single mech frame, he became worried that Master Willix would refuse to extend her services to make the Superior Mother's incarnation compatible with the core mech of the Chimera Project.
Though it was not impossible for Ves to find another consultant to do this job, he would definitely have to pay a bigger price for worse service.
Out of every mech designer that he could solicit for this job, Master Willix was by far the best and most competent choice! She would do a far better job at preserving the mounted wargear's existing strengths while adding additional power in the form of resonating abilities.
Fortunately, she acquiesced to his demand even if it didn't technically fall into the scope of their original agreement. She was only really obligated to design the core mech, which in this case was the hero expert mech that Venerable Joshua was supposed to pilot.