When a modern mechanized military comes into contact with a medieval military, the result is inevitable. And as fans of Gate: Thus The JSDF Fought There! know, nothing really ever goes wrong with expeditionary force's plans in the world beyond the Gate.
In the famous isekai Overlord, Momonga is trapped inside a shutdown MMORPG and is transported to another world as his game avatar, along with his NPC minions in the Tomb of Nazarick. Establishing himself firmly as their leader, he commands absolute authority and seeks to determine their whereabouts and what to do next.
Keyaru's early moments in Redo of Healer definitely don't go his way at all, as he is abused and injured over and over again by his perverse and heartless teammates, who view him with contempt as the lowly healer on their squad.
In a very typical isekai fashion, Seiya Ryuuguuin in Cautious Hero is given epic powers and transported to another world by a goddess tasked with saving that world. But contrary to typical isekai, Seiya doesn't set out on adventures to gain strength and learn about his new environment.
Rimaru Tempest in That Time I Got Reincarnated as a Slime becomes a slime through a random incident, but thereafter grows into the most powerful being in his new world. His plans are usually minimal and limited in scope, but always go the way he wants them.
The demon king reincarnates and goes to school. That basic premise of The Misfit of Demon King Academy is enough to produce an overpowered main character whose plans cannot possibly be thwarted, no matter how many powerful opponents, stubborn doubters, or tsundere high school girls stand in his way.
Whether he plans it all out from the beginning or just makes it up as he goes along (the latter being more likely), Onizuka-sensei helps solve his students' problems one after the other in Great Teacher Onizuka.