Well, Emeraude gifting Zagato a spirit creature (someone to be by his side and to care for him, as she couldn't?) would be a decent enough backstory in manga too...... as for surviving, well, Zagato freezing/sending him away somehow/turning him to stone when he loses to the knights but before being wounded badly enough to die (at the point where it is inevitable Innouva is going to lose, but he won't back down, because he's giving his all for Zagato - just as Alcyone did. Only while Zagato doesn't expend the energy to save Alcyone... Innouva has the connection to Emeraude, which might mean Zagato still allows himself to care about Innouva somewhat?).
Biggest question over his survival would be 'why would he want to keep on living', but an order from Zagato would be a good start? To live on, there's nothing better he can do for Zagato's sake?
.........................I also kinda want to suggest Ascot should adopt him because they're both kinda lonely slightly-broken very-loyal creatures, but that's probably an entirely different fic to the one you're planning................ XD