the necklace from the flashback will become important
Ruri was not the girl who Arma saved when they were kids. It was her sister.
The final villain will be Onigawara/Hellbrick!He seems most interested in pushing the Arma/Ruri ship out of all the characters. He could be doing that so when Ruri and Arma are too busy with each other, Hellbrick could steal most of Ruri's jewels and become insanely strong.