Uni-ball One P Red 0.5mm Ink Refill:
Its ink is specially formulated with large pigment particles that stay on the surface of the paper instead of getting absorbed into it. Since the ink isn't getting washed out by the paper, dark inks look darker, and bright inks look brighter. The ink is fast drying and bleed resistant too, so your notes will always be crisp and free of smudges.
