Type-Moon, What Do You Mean You summoned Tiamat?!
After transmigrating into the body of the Matou family's discarded child, Matou Yuu dreamed every single day of escaping the Type-Moon world.
At the age of fifteen, Yuu was sent to the Clock Tower for advanced studies. In order to use the power of the Greater Grail to "go home," he secretly slipped away to Snowfield City and joined the Holy Grail War.
But when he summoned his Servant, the system made an absurd judgment:
【Detected that the host's desire to "return home" is extremely strong!】
【Host identity: Matou family's discarded child. Mental state: An extremely mother-deprived baby!】
【Matching you with the highest-spec safe haven…】
Staring at the figure before him—Tiamat, with her massive horns, tilting her head and letting out a soft, adorable "Aaa"—Matou Yuu fell into deep thought.
My Servant… is actually pretty cute?
……
A few days later, the Holy Grail War in Snowfield City had reached a fever pitch. Ishtar, Gilgamesh, Enkidu, Ereshkigal… all the top Servants were clashing fiercely, whether for the Grail itself or out of personal grudges. Every single one of them was dead set on claiming the Greater Grail.
However, on one bright, sunny afternoon, when the Servants saw Matou Yuu casually walking down the street buying hamburgers with Tiamat in tow, they all collectively blue-screened.
Wait… What do you mean you summoned Tiamat?!
ASCodeX · Anime & Comics
Definitely the best fanfic about Tiamat in re:zreo