soo here's what its about: When timid eleventh-grader and math genius Kenji Koiso is asked by older student and secret crush Natsuki to come with her to her family's Nagano home for a summer job, he agrees without hesitation. Natsuki's family, the Jinnouchi clan, dates back to the Muromachi era (1336 to 1573), and they've all come together to celebrate the 90th birthday of the spunky matriarch of the family, Sakae. That’s when Kenji discovers his "summer job" is to pretend to be Natsuki's fiance and dance with her at the birthday celebration. As Kenji attempts to keep up with Natsuki's act around her family, he receives a strange math problem on his cell phone which, being a math genius, he can't resist solving. As it turns out, the solution to the mysterious equation causes a bizarre parallel world to collide with Earth, and it's up to Kenji and his new fake family to put reality back in order.
(from Myanimelist.net)

THIS IS SOMETHING EVERYONE HAS TO SEE
I MEAN IT HAS YOU ON THE EDGE OF YOUR SEAT, well like thirty minutes in when the story kicks in and the normal stuff is over with

but omg i love it and i now wanna change my name to "Queen Kazuma"

it's just insanely good it reminds you of Digimon the movie, one because its in a digital world
two there's something messing with the world's computer system
three its a count down to save the world

i mean it has you crying and also it's great because the action is enough where it's nothing like Black Rock Shooter OVA (too much plot not enough badass fighting scenes)
if anything i'd say IT IS WORTH IT TO WATCH! YOU CRY YOU LAUGH YOU BANG ON TABLES JUST
WATCH IT