Square Enix announced the online service end of the School of Ragnarok arcade game in Japan. According to the Twitter message and the online message the service end date is June 30, 2017 which means you can’t play with and against others from that time.
Square Enix already working on the large update the School of Ragnarok Re:Boot which going to adds new features and maybe the online service is coming back with it. But it should be noted that after June 30, 2017 you can’t use your NESiCA card or the mobile application in the game.
From June 30, 2017 you can play only local 1 vs 1 (in store), story battle and the tutorial mode.
— スクールオブラグナロク公式アカウント (@SoR_AC_PR) May 15, 2017