This is something quite different from anything I seen.
I also have one idea for you which should fit those series:

try to draw competition of 2 futanari girls where another futanari(or boy with huge dick who would make decent opponent for lucy) has her dick inside of the dick of Lucy. This is not uncommon, however, the catch is that they both cum into each other balls, their balls inflate until one of them bursts and another comes victorious, while loser has no balls anymore.