How do you get buffs on the hylian shield?

The triggers for weapon/shield buffs are linked to enemy scaling:

The reason I've brought up the previous thread is because the same mechanics that determine when certain enemies receive upgrades are also used for gradual weapon upgrades, so it's a good idea to have a grasp on them before reading this.

This answer can give a crash course on how this works.

The first thing to account for is modifier scaling:

Getting into the meat of things, weapons typically upgrade as such: No modifier-->blue modifier-->yellow modifier-->stronger variant (if applicable)

There is also class variation to account for:

Because two-handed weapons and spears play very differently compared to the standard one-handed sword, with the former being slow but powerful and the other being weak but fast, their strength thresholds for upgrades differ.

And thirdly, there is weapon tier scaling:

The third influence applies to weapons that can change into better weapons. I am not entirely sure how big an influence it is, but it would seem that weapons tend to change earlier or later depending on the strength of the better weapon.

For instance, the Soldier's Shield becomes the Knight's Shield much later than the other Soldier tier weapons change, and the Knight's Shield has a much higher proportional strength than the other Knight tier weapons.

So, gaining an understanding of the "point system" can be useful to gain an understanding of when this modifier can be applied to the weapons you use. The Hylian shield specifically is the last weapon to receive modifiers:

1400.2 Points:

• Royal Guard's Spear (Blue)-->Royal Guard's Spear (Yellow)

1500.2 Points:

• Hylian Shield-->Hylian Shield (Blue)

1883.4 Points:

• Hylian Shield (Blue)-->Hylian Shield (Yellow)

Enemy Scaling in BOTW

Weapon Scaling in BOTW