Friendship
That's what I absolutely love ❤ was the deeply ingrained friendship between two prison convicts - Red & Andy. Both grew to trust each other and Andy admitted a lot of things to Red, most noticeably his pieces of a puzzle to an escape attempt. Red took that in good faith, followed the clues and got happily reunited with his friend in a tropical paradise.
That was deep loyalty right there and it's very heartwarming. The only other story depiction I can remember for undying friendship loyalty is "Watership Down". Those were rabbits, but it's humans that are depicted here. Regardless of what you are though, a loyal and trusted friendship is the most important thing of all.
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Come to Middle-Earth, a world beyond the furthest reaches of your imagination