Ruri is from ASH (Actor's School Hiroshima) where Riho also came from. She actually auditioned for H!P in 2017. More pics on that site.
Great to have another Hiroshima ASH graduate on board, making at least three into H!P. Of course, the most famous ASH grads are the three members of Perfume, so the H!P girls from there are in good company!