Obligatory shitty response>Demon King fucked up reality a long time ago before being defeated>As a result, demonic corruption is always leaking into the world and people from earth occasionally get Isekai'd>MC and Girl both get Isekai'd. The fantasy world is mostly medieval fantasy but with anachronistic things such as breech loading rifles and Victorian architecture, etc>The Duo get picked up by the guild when the Girl accidentally discovers she can use magic. Magic is powerful and rare as shit for humans and the Empire conscripts all mages>MC gets conscripted along with her because he's a person of interest to the Empire >They're both assigned as apprentices under a Knight and Mage. They train in combat, learn about the world, help/join local guilds, meet and befriend other main characters and such>Lots of comfy shit>In the background however, tensions regarding succession of the Empire's throne arise between his three children>Eventually, the Emperor dies and a succession war breaks out. MC and Group get dragged into it led by the third born daughter to the emperor>While the war goes on, the rate of corruption leaking into the world starts to spike, foreign powers start declaring war on the Empire, and separatist rebellions start taking place>Whole continent goes to hell and the MC and his faction try to claim the throne, reunify humanity and salvage the situation for themselves and the world before its too late
MC/Girl motivations are to get home at first but as they save/meet people, live in the world, and fight in the war, their motivation changes and they decide that this new world is their home.
Near the end they find the opportunity to return to Earth but both refuse because they can't abandon the new world.