Okay, I know 'relatable' gets thrown around a lot, but for me, a strong isekai protagonist isn't just about being overpowered. It's about having a clear moral compass that feels earned and seeing them wrestle with the consequences of their new world. A lot of protagonists are just blank slates for wish-fulfillment, which is fine, but it doesn't create that lasting connection.
Take Rudy from 'Mushoku Tensei'. He's deeply, profoundly flawed—his past life baggage is a central part of his character. His strength grows slowly, painfully, and his journey is about becoming a better person, not just a stronger mage. Watching him fumble, make terrible mistakes, and genuinely try to improve is what makes him compelling, even when you want to shake him. It’s not a comfortable relatability, but it feels real.
On a completely different note, you have Myne from 'Ascendance of a Bookworm'. Her strength is pure, stubborn passion for books, and her entire struggle is against the physical and societal limitations of her frail body and medieval-esque world. Her 'cheat' isn't combat; it's knowledge, and her drive feels so authentic because it's born from a love any reader can understand. Her victories are small, logistical triumphs—getting paper, making a printing press—and they're incredibly satisfying.
Then there’s the pragmatic, world-weary kind of strength. Cid from 'The Eminence in Shadow' is hilarious because his 'relatability' is that of an unhinged theater kid whose chuunibyou delusions accidentally become reality. You don't relate to his power, you relate to the absolute commitment to a bit, taken to a catastrophic extreme. It’s a parody of the trope that ends up being weirdly endearing.