Multiverse: The Second Dimension Is Actually Myself

(A novice-friendly and purely entertaining multiverse story, no criticism please.)16-year-old You Ming received a Command Seal, becoming a participant in the Holy Grail War. Immediately, he began to summon his Servant.But the system awakened at the same time, Servant and system appearing together, causing a serious BUG!What's even stranger is that the detective agency he inherited from his parents also gradually became strange."Kibutsuji Muzan, you're so beautiful!""Tatakae (Fight)! Take down this Gillian!""Aizen! You won't get away!""The natural gas in the neighboring city of Fuyuki is about to explode again!"P.S: This book is a mixed pot of anime worlds, the timeline is the end of the 20th century.