There is one unironically Good One: "His soul goes marching on in another world". It's an Isekai with famous abolitionist John Brown as its protagonist, and he's just as dead-set on ending the institution of slavery in fantastland as he was irl. No excuses, no handwringing, just pure, righteous action.
I think my favorite weird slave thing in a manga is this one 'kingdom builder' story where a guy is isekai'd to a fantasy kingdom as a Prince and he buys fuckloads of slaves.
Like... he first buys around 50K slaves to build up a territory into a fortress city and then he buys another 50K to help build war machines, and then finally he buys 100K to make into a private army. And it just strikes me that the author probably has no clue about human beings beyond Sims City because there's no way in hell any random slave trader would have 200K+ slaves in inventory. Not to mention the sheer logistical nightmare of transporting, feeding, clothing, and then training 200K people let alone slaves who are being wrangled by maybe 10 people including the Prince.
All of this in the capital city where the standing military force is listed as around 65K total...
John Brown's body lies a-mouldering in the grave, John Brown's body lies a-mouldering in the grave, John Brown's body lies a-mouldering in the grave, But his soul is marching on!
Being honest the slave companion trope is just a lazy way for the autor to give the protagonist a party without having to develop the story to a point that people following the protagonist make sense. Its kinda backwards actually, it made the characters follow the protagonist and just later give a reason to why they should do that.
There needs to be an Isekai with a John Brown-esque protagonist thrown into a world full of slavery where each episode he kills slavers, frees the slaves and builds up and army of freed slaves who continue killing even more slavers.
Shoutout to the person who wrote that isekai webnovel where famed abolitionist John Brown gets transported to an isekai world with slavery in it and, true to form, decides to end slavery.
I find hilarious when an isekai tries to use the but I am nice to my slaves argument. Okay sure you aren't actively abusing them, but they're still your possession, they have to follow and obey you, and are dependent on your generosity to survive. What you've essentially got is a pet, you're keeping a person as a pet.
I really need the author of Frieren to write an Isekai. Deconstruct some of its tropes, fully embrace some of its tropes, present it all with deeply human character writing. Y’know, just like Frieren does with classic “Hero’s Journey High Fantasy”.
8:05 damn imagine having to risk a civil war to end slavery or even having to actually have a civil war to end slavery its not like that ever happened or anything