It's not magic. Sealing isn't magic at all. It's mathematics and barriers and cold, unflinching rules and how far can they bend the concept of a barrier until it does what they want. It's a puzzle with pieces that have to be invented on the go, and perfection in handwriting comes at a loss of efficiency.
Looking good is just as important as being good. Yayoi has a natural talent for writing the seals with brush and ink. Kirara needs to sew them down. Raiko can place hers with a touch.
Raiko's are the best.