Legend can't die and it's all Hylia's fault prompt / headcanon;
Once her hero died (Time) Hylia became more impulsive, focused on making sure her hero's alive to fulfill their duty. Her obsession didn't happen immediately though, the process was gradual:
She started to aid Legend in his journey in the tiniest but allowed for her ways (manipulating the light source so it's shining away / on something he has to notice, making sure the water flow where he wants to step isn't as strong at the rest, etc.) which could go unnoticed and mistaken for beginner's luck;
Later on, as he realized, Legend's spirit to adventure was something she couldn't' contain. The more time passed, the more lenient Hylia became with things she shouldn't do but still allowed herself to (her tips where he should go first became more clear, she personally intervened when he had to make a harder decision, she wasn't beyond speaking to him through his mind, etc.);
And, y'know β At first it wasn't with any intention of malice, she just wanted to help to her best possibilities her hero to ensure Ganon (or someone else) wouldn't get his hands on the Triforce, etc.;
But later on, the more time passed, Hylia noticed something... Peculiar. Legend didn't only posses the Triforce of courage that have him its own benefits, he was also intelligent;
And THAT lead Hylia to testing her hero rather than simply helping him;
She became more and more intrigued by seeing how her hero would do against the hardships she threw at him (the previous light that helped him now pointed monsters in the direction his camp was, the bursts of energy that helped him keep going were far and less present) that she became slowly obsessed with the thought of shaping him into a perfect hero;
A hero that would carry on his legacy and make sure no evil would be able to roam these lands safely without fearing Legend's name.
TL;DR β Hylia in the downfall timeline from helping her hero became obsessive with the thought of creating the "perfect" one, making her slowly changing her methods from aiding Legend in battle to putting him at more risk.
But! Where's the part where Legend can't die? Wellllll, here it is!
It's not that Legend is immortal, it's that he became so prepared to stay vigilant for everything that's about to come that he knows when something's about to strike, etc. He, against his own will, was slowly shaped into exactly what Hylia wanted β a soldier that'll carry her duty.
Because of the experience he's just REALLY hard to kill, although there for sure was more than one situation with a close call (Legend has no proof though that Hylia didn't interfere with him miraculously keeping it together for longer than it should've been possible. And even if he had β how could he complain to her? He did want to live).
And so at some point it became obvious β Hylia's no longer on his side. She wants a perfect soldier, vessel for the hero's spirit to live in him and do his job properly.
It's an endless game of Hylia getting what she wants because there's no one who can stop her β a literal Goddess, β from doing whatever she wants. It was her job to maintain the balance between her duty as a Goddess and the mortal she chose, she is failing and she knows it. She just pushes it aside for the sake of "greater good" she believes she's doing it for.
Legend's adventurous spirit with time became a burden; he became bitter because they weren't anymore about discovering the secrets of the world, what it had to offer, etc. It became a game of "What Hylia will throw at me this time that will make me barely live".
He claimed he's retiring but he knows it's not happening, sooner or later he'll get out of the house because he can't sit in one place for too long (and because Hylia's becoming desperate and impatient) ALTHOUGH, this time it was adventure that knocked on his door's; The Chain!
BONUS POINTS for Hylia getting frustrated and angry at Legend because he dared to go through the portal (or the portal came for him, dunno) and answer the call of a different iteration of hers.
She's so far deluded in her possessiveness over Legend that she thinks SHE created the veteran he is today β and she's not going to stop anytime soon in her antics.
