I'll try that when I get some art pens, an excuse to go to 'Art Friend'. Visiting the 'Art Friend' art shop is a fun experience lol, I usually get stuck in the shop for a long time sketching around with all those sample drawing materials.
There'd probably be drawing sessions in pen sometimes in the animation course, if not I probably won't try much drawing in ink. Because I know I would be very addicted to drawing on tablet lol
My art classes last time always taught pencil only drawing and I learnt pen prawing only in design class where we draw objects. I'm way too used in pencil drawing, I've been doing it like 15 years or more lol, but I switched to mechanic pencil like halfway, because I'm lazy to sharpen.
You should try inking and cleaning some sketches in the future (not that your graphite sketches aren't extremely clean already, very nice!) to get a taste for it, it can really add a lot to the appearance of the piece.