Oracle Text

O-Naginata can be attached only to a creature with power 3 or greater.

Equipped creature gets +3/+0 and has trample.

Equip 2 (2: Attach to target creature you control. Equip only as a sorcery.)

Card Rulings

6/1/2005 O-Naginata becomes unattached if the equipped creature’s power is less than 3 as state-based actions are checked.