It’s a brushset for glittery lines.
They’re not necessarily gold, you can change colors.
Highlights and brushsize are controlled with pen pressure.
Feel free to adapt them in any way you want ^^

There are also metal ribbon brushes:
https://assets.clip-studio.com/en-us/detail?id=2175340
https://assets.clip-studio.com/en-us/detail?id=2175564

Gold Line