So we already have Ciel, Dobryna, and Xu Fu as the confirmed summer servants. Count Summer Eresh if you will.
We also got the male servants: Karna, Percival, and Bartholomew Roberts
We're guaranteed to see four more summer servants: a five-star and two four-star, plus another one - the welfare (another four-star).
Common speculation is the five-star will be Summer Koyan...
I can't disagree since she seems overdue to get a summer form.
I also think there is an "Indian" theme to this summer given the clear requirements (must clear Ordeal Call 0) and Karna being a part of it.
So my other picks are Lakshmibai and a surprise servant... Sita.
Yes, Sita from Arcade will join FGO through summer and be sort of like Lady Avalon where she has a summer outfit and a regular outfit. But she'll be a four-star instead of five.
And Medusa will be the four-star welfare.
