This series touches on a lot of the depths of the human condition, simply because its main character isn't human and exists to learn and understand humanity. The unfortunate reality in Fushi's existence is the sole aspect that makes life, life: it ends. He experiences it now, twice, in very grim and heart-wrenching situations. This series, and all props go to the studio for not only being faithful to the manga but expounding on it and adding a layer of emotion that only works through a cinematic experience, is truly a world beyond the levels of emotion that most shonen delve.
In terms of lore, I would put this on the level of Made in Abyss, and in terms of depth of character I would put it close to One Piece (which is notorious for having some of the deepest and most traumatic backstories in all manga). To Your Eternity truly goes well beyond the conventions that so many manga and anime fall victim to, and it does it with seeming ease (although I can't imagine if this solitary episode is as soul crushing as it is to a ~casual~ viewer, what writing must have felt for the mangaka who has actually lived these characters' lives in their head.) Simply astounding. 10/10.