FWIW the artist mentioned using a nib pen in post #6873008, though I can't say with 100% certainty that it's also used here.

岩戸鈴芽 said:

FWIW the artist mentioned using a nib pen in post #6873008, though I can't say with 100% certainty that it's also used here.

I think you can tell they're using nib pen from how the ink spreads on Ayaka's hair. The blots are rather uneven, unlike if you used a brush.

Rathurue said:

I think you can tell they're using nib pen from how the ink spreads on Ayaka's hair. The blots are rather uneven, unlike if you used a brush.

That sounds about right, thanks for weighing in.