Ancestral Katana is a common Artifact — Equipment card from Kamigawa: Neon Dynasty (NEO), collector number 1. Current market price: $0.23 (foil $0.32), TCGplayer market prices via Scryfall.
Whenever a Samurai or Warrior you control attacks alone, you may pay {1}. When you do, attach this Equipment to it. Equipped creature gets +2/+1. Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)