I think the emotional tension with Sorey and Mikleo gets built from a few really solid foundations in the game 'Tales of Zestiria'. They've got that lifelong childhood friend bond, which is already ripe for unspoken feelings, but then you layer on the whole Shepherd and Seraph dynamic. That creates a built-in conflict of duty versus personal desire. Are they partners first, or something more? A lot of fics I've read play with that professional closeness blurring lines, the fear of what a romantic relationship might do to their sacred duty.
Then there's the immortality question. Mikleo's a Seraph; he's not aging like Sorey will. Fics that look beyond the game's ending have to grapple with that. The tension isn't just "do they like each other?" It's "if we do this, one of us will have to watch the other grow old and die." That's a huge, tragic weight to carry, and writers who dig into that create some genuinely heartbreaking and beautiful stories. It forces conversations about sacrifice and the value of a mortal lifetime.
My personal favorite fics are the ones where the tension is quieter, though. Not big dramatic confessions, but the small moments—Mikleo noticing Sorey's habits changing over the years, or Sorey feeling a pang of something he can't name when Mikleo talks about the ancient past. That slow burn, where the emotion is in what they don't say, feels truest to their characters.