Not sure if you knew this OP but angel konan, shisui, hot blooded kushina, and edo hiruzen appear in time-limited recruitment about every two weeks for past several months on the China server. Out of the four ninjas, two will be present and they alternate every time the event appears, and you'll be able to get free frags for that week from points gained from using stamina and since the event is frequent, you can slowly build them. Hopefully, Oasis decides to copy what the China server is doing when they get to that point of what is doing.