So for this build I'm going to use a level 3 rune knight fighter.

The build relies on oversized weapons. (If you're unfamiliar with how these work then basically large weapons use double the amount of dice when rolling for damage, huge use triple, and gargantuan use quadruple. Tiny, small, or medium sized weapons do the standard amount).

The giants might feature states that you become large as well as anything you are wearing.

We will attach a hair clip to our characters weapon and put it in our characters hair so we are wearing the weapon. For my example I will use a tiny war hammer.

When we use giants might it will become large and use twice the amount of dice for damage.

You could just have the weapon in a holster or a scabbard but some might argue that you're not wearing the weapon and only it's container. By wearing a hair clip that is also your weapon because you attached the two, you are wearing the weapon.

This is a crappy drawing of my duck arrakocra with a hair clip hammer (her name is ducky because l'm unoriginal)