Finding a Flesh Lily for Yu'er is the first sidequest you'll encounter in Phantom Blade Zero, but you can't complete it until a few areas and bosses later.
You can find the Flesh Lily below the Sha-Chi tower, an area you reach after arriving at the outpost and beating Peng Meng. Specifically, it's accessible from the Valley Sha-Chi Tower 1st Floor bell when you arrive at the base of the tower, though you'll have to fight a boss to get it. Follow the video above, or:
