All three movies are directed by Mari Asato (Ju-on: Black Ghost, Keitai Kanojo) and their events take place at the same time in different locations.
The Real Onigokko franchise is based on a novel by Yusuke Yamada about a parallel world where everyone with the last name "Sato" is hunted by masked men for some mysterious reason. "Onigokko" is the Japanese equivalent of the children's game "tag". The person designated "oni" (demon) tries to catch any of the other players. Appropriately, these movies generally stick to the basic theme of people being chased. Fighting back is rarely an option due to the single-minded determination of the "oni", so survivors end up running for their lives in a series of nonstop action scenes. In a similar vein to Battle Royale,