Blitz Battle! The Three Admirals was an event that occurred on 10/24 19:00 PST~10/26 18:59 PST 2017.
It was composed of three events:
- 30 stamina Blitz Batle! Vs. Akoiji
- 35 stamina Blitz Batle! Vs. Kizaru
- 40 stamina Blitz Batle! Vs. Akainu
See overview on reddit.
Those battles were rerun on April 29 - May 1st 2018 as part of the Rankings quest.
Official ranking / reward page: http://gb.trecru.channel.or.jp/battle-royale/marines/en/?user_id=