Inuyasha
Back then i didn't even knew it was "isekai", everything feels so natural and their interactions were easy to accept. Especially when she can just go back and forth, it feels like an extension of another place.
Watched it during 2000s, and i just graduate from "shonen" animes, and have yet to find any seinen. I didn't even know the existence of "Hentai" at that time.
Then i focus on my study life, and didnt watch any show at all. I got into tunnel vision of study for quite some years.
After years of continuous busy study life, finally able to watch shows again.
Then i also watched "SAO", which i still didn't know was Isekai. In my opinion, They're just player stuck in VR game with other player, not actually "different world".
Then i watch absolutely no other isekai.
Ans finally, My first real "isekai", knowing it was "isekai", is "Reincarnated as Slime".
There's simply no denial that MC is reincarnated in another world, and aboslutey no going back. It was quite lighthearted, and therefore easy to watch.
Then i watch Mushoku Tensei, which is "The best isekai experience". It really feels heartwaming and evokes my childhood joy of restarting as a better person.
After that, "Re Zero" and "Konosuba", which is very very goood.
Then i tried "Reincarnated with smartphone", before i realized how horrible it is and so I drop really hard.
I can't stand the MC didnt get beaten up by the thugs like Subaru from Re:Zero.
Noe i could stand the MC didnt get realistic hard times and struggle like Kazuma from Konosuba.
Pretty much the effect of watching the parody first before the real ones.
I could understand Rimuru as he's already OP even when he first summoned, but there's still some other type of struggle you cant just solve even with power.
Then I watch "Overlord" and "Tanya the Evil", and i regret not watching it back in the days when i skipped them.
I also watch "Welcome to Demon School!! Iruma kun", which really feels like pre-SAO isekai.
Then some other shameless Overlord clone like skeleton knight, which didnt get far.
And then "Reincarnated as sword", its very heartwarming and has good "battle" and "slice of life" balance.