User blog comment:FgoMinami/Possible Future Events/@comment-115.178.218.46-20170424182043/@comment-27971189-20170425044538

On interview, Shiokawa said that the Summer Units of 2016 were based on popularity poll among DW and TM staffs.

DW's is the first batch (Anne, Kiyohime, Tamamo, Mordred) while TM's is the second batch (Arthuria, Martha, Marie) with Scathach representing most popular female character among players hence welfare.

Conclusion, after all, that depends on how DW and TM will did it.