Back in 2015 it would usually take me 2 hours to get to school and there's no service on my phone at certain places so I decided to download a drawing app and just kill time. The one that I used is called Tayasui Sketches(wouldn't recommend). It had only 4 layers in total and you need to pay for extra brushes(which I did but never actually used). But now it has unlimited layers(I think it's free). And within the 6 months I had after downloading it, I did these 2 drawings(Miku and IA). Keep in mind that I only had 4 layers to work with so all the colors were actually on one layer and these were done by fingers.
(ignore the 2 random lines)
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From @jeembob