Ignia’s basically guild royalty, but he’s never going to show up for the paperwork. He’s the son of the Fire Dragon King Igneel, so his ‘role’ is more like a legendary figure you’d put on a tapestry, not someone you’d expect to be sorting out mission requests. In the actual daily hierarchy? Zero. He’s not a member, he doesn’t take orders from Makarov or anyone, and he operates on a completely different power scale.
That said, his presence warps the hierarchy just by existing. When you have a being that powerful casually linked to Natsu, it creates an unofficial, unspoken tier above the S-Class. He’s a nuclear option that the guild doesn't control, but whose mere association grants Fairy Tail a kind of unassailable, mythic weight. It’s like having a dormant volcano in your backyard—it doesn’t tend the garden, but nobody’s going to mess with your garden.
Honestly, I think his real ‘role’ is as a narrative foil and a looming threat-turned-ally for Natsu. He’s outside the guild structure because his conflicts are on the level of dragon gods and elemental primacy, not bar brawls and dark guilds. The hierarchy is a human thing; he’s playing a different game entirely.