Sadako vs Kayako (2016)

According to Anime News Network, Sadako vs Kayako was originally a April's Fools joke. The movie was later confirmed to be real in December 2015. The movie will be released in Japan on June 18, 2016. Kōji Shiraishi directed it.

Sadako Yamamura and Kayako Saeki (Takako Fuji) finally meet after two friends Natsumi (Aimi Satsukawa) and Yūri Kurahashi (Mizuki Yamamoto) watch Sadako's cursed video in an abandoned house under Kayako's curse. Sadako and Kayako soon fight each other.

A university professor named Shinichi Morishige (Masahiro Komoto) investigates Sadako's cursed video. A young woman named Suzuka Takagi (Tina Tamashiro) is also cursed by Kayako. She becomes cursed after she explores the abandoned house under Kayako's curse. There's also a spirit medium named Keizō (Masanobu Ando). Misato Tanaka plays Fumiko Takagi, Suzuka's mother. Kayako's son, Toshio, will also appear in Sadako vs Kayako.

Sadako vs Kayako will most likely be about Sadako and Kayako battling each other to see who gets to kill Natsumi and Yūri. Since Sadako's cursed video was played in a house under Kayako's curse, it's possible the fight between the two onryō (or, vengeful spirits) is influenced by Sadako's accidental trespass into Kayako's house. Kayako could be protecting her property.

To learn more about Sadako vs Kayako, check out:
http://sadakovskayako.jp/ (Japanese)
http://sadakovskayako.tumblr.com/ (Japanese)
https://www.instagram.com/kayakowithtoshio/ (Japanese)
http://natalie.mu/eiga/news/177274 (Japanese)
http://www.crank-in.net/movie/news/40312 (Japanese)

http://www.animenewsnetwork.com/news/2015-12-10/sadako-vs-kayako-film-brings-together-ring-ju-on-franchises/.96308 (English)

http://www.animenewsnetwork.com/news/2016-02-24/ring-ju-on-crossover-film-sadako-vs-kayako-reveals-new-teaser-cast-june-opening/.99023 (English)

Sadako vs Kayako IMDB (English)