It has been a manananggal representation throughout the movie. As shown in their school performance, Raissa is the upper and Jo is the lower half. But also, Raissa's whole theme is flight or to soar (wings,rocket).
While Jo's entire theme is the one who is grounded (shoes,rock).
Jo was actually so funny talking abt "who will Raissa choose - the weredog or the merman" when she knew her homegirl was bent since they were like ten. whole time she wrote that manuscript they were already making out on the down low