Phantom Blade Zero has a seemingly endless amount of collectibles for players to find. Memory Flowers, Quick Hand Treasures, Medicines, Phantom Edges, and that is far from an exhaustive list. However, there are some smaller collections that are tied to one specific area. In this case, the Ribbons are tied to trees around the Village of Lu.
These are tied to the Young Mistress questline, and you will need to collect all five before you find the final boss of the chapter to reap the rewards.
Finding all five Ribbons adds an additional phase to the fight with Mu Xiaokui, which admittedly makes the fight a bit harder, but also grants you an additional reward. Those who find all Ribbons will gain the Fiend Saws as well as the Wild Oriole Sword for winning this fight. It's simple math: two weapons are better than one. So, you'll want to peruse the Ribbon Locations below.
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All Ribbon Locations
As soon as you enter the village of Lu, you should be on the lookout for these Ribbons, which are tied to trees around the area. Here are all the locations you'll want to check out:
Ribbon #1

Admittedly, the first Ribbon is a bit of a gimme. Soul's gaze will be drawn to this the moment you set foot in the village. This is the area nearest to the Well of Three Puppets Bell. You'll find this tied to a tree right of the footbridge.
Ribbon #2

The second Ribbon is located on the other side of the Covered Bridge, which will initially be inaccessible until you clear the red thread blockade. This is done by taking the path just right of the slope that drops down from Quick Hand Zhang's Hideout. Use your Dread Axe to get through and then defeat the enemies in the area to clear the way.
Then, head back to the Covered Bridge, use your Sickle to get to the other side, and tied to the bridge you'll find the second ribbon.
Ribbon #3

The third Ribbon, much like the first, is pretty much impossible to miss, as you'll gain this one after you defeat Master Bi Yuan and activate The Lady's Grounds Bell. This is an automatic pickup, so you don't need to search the area for a Ribbon.
Ribbon #4

Your next stop is the Temple of Blue Butterflies. This is accessed by heading to the Well of Three Puppets Bell and then heading over the river behind, where you find the 'A Dream of Motherhood' quest giver. Then, when outside the blue glowing temple. You'll find a Ribbon on a tree left of the entrance.
Ribbon #5

Your last Ribbon is obtained not long before the pivotal fight against Mu Xiaokui. When you gain access to the Well by progressing the main quest, you'll want to jump down there and work your way towards the Beneath the Well Bell.
Head into the room directly to the right of the Bell, and along the wooden walkway attached to a pillar, you'll find the last Ribbon for your collection.

After you complete the set, you can then go ahead and ride the lift up to the Lakeside, where you'll fight Mu Xiaokui, and you'll gain the Fiend Saws when the fight concludes.