[March 22 updated]
ATTENTION: Some Xiaomi devices need to be RESTARTED after the setting being changed, or you might run into force close when you redownload the game!!!
Tips for those who had "invalid apk" problem while you installing: You need to turn off *MIUI Optimization* in the phone settings (works on Mi phone).
7. REDOWNLOAD the MASS FOR THE DEAD and you can install it!!!
Open Developer Mode may cause some unexpected problems, but you can turn on MIUI optimization and turn off developer mode after installing the apk. It won't effect the game.
Hope it helps you guys! Android phone is kinda troublesome indeed, but we like it anyway coz there are some many japanese games we can play!!