This version of Vault Boy is part of a wider crossover between multiple worlds.

Boy: "Well howdy there, stranger! I'm the Vault Boy, and I'll be representing Vault-Tec for all of you interdimensional adventures roaming the wastes! And this here is my lovely assistant, the Vault Girl!"

Girl: "Hello hello!"

Boy: "So what'll it be? Say the word, and we'll make it happen, here at Vault-Tec!"