This vinyl pencil pouch by Monster Circus has a cool triangular shape, flattened at one end and curved at the other. She shares a tutorial showing how she did it. Go to her blog for the tutorial. (Link is an English translation.)
[photo from Monster Circus]
Monsterscircus says
Wow, Anne! Thank you so much for sharing my pencil case, really so kind of you! And what a treasure chest your have here, so lovely blog universe you have here! Have a great weekend and thank you 🙂