Dungeons & Dragons Templates!
I hope I am speaking on behalf of the gaming community when I suggest this: It would be fantastic if you were to partner up with Wizards of the Coast to acquire usage rights in creating a Rocketbook with blank Dungeons & Dragons character sheets (5e).
I. Cannot. Stress. How. Much. Trees. Would. Be. Saved!
It would be a substantial niche to get into, and I would love to hear the outcome of this if you pursue reaching out to them.
Attached is an example 5e blank sheet.