A new event, Sea Monster Crisis: Floating Island of the Innocents, will go live in Fate/Grand Order from April 6, 2022. This means that it will start more or less as soon as the ongoing Battle in New York 2022 ends. While the Sea Monster Crisis event will give a welfare Servant, there is no information as of yet.
In order to participate in the event, you will need to first finish Lostbelt No. 2. However, though you will not need to clear Lostbelt No. 6, the event will contain spoilers for that chapter. As per usual, the welfare Servant that you can get from the Fate/Grand Order event will be an SR.
In addition to the free Servant, there will be a new Servant to pull for from the gacha. Their name is simply Nakayoshi Saber, and they are two Servants acting as a single unit. There is speculation that Nakayoshi Saber is the Trung sisters from Vietnam. Take, who worked on Pokemon Sword and Shield, Katanagatari, and Pokemon Legends: Arceus, designed Nakayoshi Saber.
In addition to the new Servant, Lasengle also revealed which characters play an important part in the event story. These Servants include Morgan, Mysterious Alter Ego Lambda, Semiramis, Meltlilith, Wu Zetian, and Ereshkigal.
Fate/Grand Order is available on mobile devices, and the Sea Monster Crisis event will go live on April 6, 2022. More information on the welfare Servant, as well as how to play the event, will appear in the near future.