Gordon Freeman

After Gordon Freeman manages to destroy the Citadel's reactor and defeat Wallace Breen (the Combine Empire's designated leader of Earth), before the fire from the explosion reaches Gordon, G-Man (who serves as the supervisor, employer, and enigmatic observer of Half-Life) freezes time and appears before Gordon, telling him that he did a great job, congratulating him and stating that his actions had far-reaching consequences. However, before taking Freeman away and placing him in a state of suspended animation, he decides to take him to a quieter universe so he can relax before Gordon enters his state of stasis (I'm not sure if G-Man can take characters to different universes, but well, I think he can). G-Man teleports Freeman to the world of Girls und Panzer, so he can calm down a bit.

Gordon Freeman appears in the middle of a forest, alone and lying on the ground, with his typical crowbar in hand and his gravity gun by his side. Freeman stands up, slings the gravity gun over his back, and begins to explore the forest. In doing so, he sees flat terrain and a military tent, next to which several WWII tanks were stationed. There were no Combines, and it seemed like a peaceful place. Freeman felt calmer; he slowly approached the tent and heard that inside, there were some high school girls. They were the main commanders of almost all the Sensha-do tank academies (such as Miho Nishizumi and her older sister Maho Nishizumi, Erika Itsumi, Darjeeling, Katyusha, Nonna, Anchovy, Mika, Nishi, Kay, etc.) planning a sort of tactic to win the Sensha-do match against a university academy: All-Stars, commanded by Alice Shimada. While they were deciding on the tactic to use, Miho spots Gordon through a small window in the tent; she thinks he is lost and wants to help him.