MC gets lost on the way to the kitchen and ends up face to face with Zelretch. In exchange for doing the old man an unspecified favor, he is allowed to transmigrate to the world of One Piece with nine Servant Cards and a unique Devil Fruit, the Mana-Mana-no-Mi...
(A/N: This list took so damn long to make...)
[Saber]
Grade 1: Jason
Grade 2: Chevalier d'Eon
Grade 3: Gilles de Raise
Grade 4: Bedivere
Grade 5: Mordred
Grade 6: Fairy Knight Gawain
Grade 7: Arthur
Grade 8: Yagyu Munenori
Grade 9: Unknown
[Lancer]
Grade 1:Gareth
Grade 2: Leonidas
Grade 3: Hector
Grade 4: Diarmuid Ua Duibhne
Grade 5: Cu Chulainn
Grade 6: Fairy Knight Lancelot
Grade 7: Ereshkigal
Grade 8: Karna
Grade 9: Unknown
[Archer]
Grade 1: Billy, the Kid
Grade 2: William Tell
Grade 3: David
Grade 4: Euryale
Grade 5: EMIYA
Grade 6: Fairy Knight Tristan
Grade 7: Ishtar
Grade 8: Gilgamesh
Grade 9: Unknown
[Caster]
Grade 1: Mozart
Grade 2: Charles Babbage
Grade 3: Paracelsus von Hohenheim
Grade 4: Avicebron
Grade 5: Medea
Grade 6: Nitocris
Grade 7: Queen of Sheba
Grade 8: Merlin
Grade 9: Unknown
[Berserker]
Grade 1: Frankenstein
Grade 2: Asterios
Grade 3: Beowulf
Grade 4: Penthesilea
Grade 5: Heracles
Grade 6: Ibaraki
Grade 7: Lancelot
Grade 8: Arjuna
Grade 9: Unknown
[Assassin]
Grade 1: Mata Hari
Grade 2: Kato Danzo
Grade 3: Jack the Ripper
Grade 4: Stheno
Grade 5: Hassan-i Sabbah (Variable)
Grade 6: Shuten
Grade 7: Kama
Grade 8: Koyanskaya of Light
Grade 9: Unknown
[Rider]
Grade 1: Bartholomew Roberts
Grade 2: Edward Teach
Grade 3: Habetrot
Grade 4: Medb
Grade 5: Medusa
Grade 6: Achilles
Grade 7: Ivan the Terrible
Grade 8: Quetzalcoatl
Grade 9: Unknown