Mercedes-Benz 300SL

A toy that Kiritsugu bought for his wife, in order to enlighten her about the wonders of modern science.
…Well, it's sort of an old-fashioned choice as far as education is concerned, but I'm sure Irisviel must have preferred it that way. Since it was customized by Kiritsugu, you might expect it to be decked out with machine guns, missile launchers, ejector seats, and oil slicks, but it isn't. Probably.
After the war ended, it was stashed away in the castle on the outskirts of Fuyuki, where happily it was eventually inherited by Illya.
By the way, in Japan it is well-known as the actor and singer Ishihara Yuujirou's favorite car.

Fate/Zero material: Fate/Zero Encylopedia