Sun, the Champion of the Alola region, was tired. Tired of the rematch, Tired of most of his friends behaviors(they were just starting to get annoying), and tired of all the stress of it all. He needed a Vacation! So he had Nebby take him to a world with no pokemon or trainers. He has taken stay in the town Fuyuki in the island Nation of Japan.

During his stay he walked down the street during a calm downpour, which often helped his stress. He heard a grunt in a Allyway and went to investigate, there he found a cloaked woman laying on the floor in exhaustion, all while looking like she was about to disperse into light molecules. He immediately went to her side to help. This was Medea, a Heroic Spirit of the Caster Class. Sun used his aura(which he had trained enough to heal, sense targets, and enhance his reflects) and poured it into her, which stopped her from glowing.

The rest of the servants, besides  Berserker, Rider, and Caster, have not been summoned yet. And Sun's Aura acts as a much more effective power source then Prana, which makes Sun easily able to call multiple Servants.

Team(Pokemon)
-Torana (Incineroar)(Darkness Lariat- Thunder Punch- Flame charge- Fire punch)

-Philip(Mr. Mime)(Moon blast- Psychic- light screen/protect- metronome)

-Echo (Noivern)(Boom burst-Dragon pulse-Dragon claw- Steel wing)

-King (Empoleon)(Steel wing-Aqua jet-ice beam-Scald)

-Mari (Sylveon)(Moon blast-Fairy wind- Shadow ball- Bite)

-Nebby (Solgaleo)(Flash cannon- Psyshock- Crunch- Sunsteel strike)

Heroic Spirits
Saber: Mordred (Sun)

Lancer: Lartoria/Elizabeth Bathory (second Accidental Dual Summoning during second summon)(Sun)

Rider: Medusa (Sakura)

Caster: Medea/Tamamo No Mae(Medea wanted to see if Sun could summon another servant from an already summoned class, and it worked)(Sun)

Archer: Euryale (Rin)

Assassin: Jack The Ripper/Carmilla Bathory (accidental Dual Summon from first attempt at summoning)(Sun)

Berserker: Frankenstein's Monster (Illya)