O-Naginata
Artifact — Equipment
This Equipment can be attached only to a creature with power 3 or greater.
Equipped creature gets +3/+0 and has trample.
Equip 
(: Attach to target creature you control. Equip only as a sorcery.)
Brian Snõddy
Saviors of Kamigawa (SOK)
• #157Rulings
O-Naginata can become attached to a creature only if that creature's power is 3 or greater before O-Naginata is attached to it.
(wotc • 2020-08-07)
O-Naginata's equip ability can target any creature you control—but if the creature's power is 2 or less, it won't become attached as it resolves.
(wotc • 2020-08-07)
O-Naginata becomes unattached if the equipped creature's power is reduced so that its power is 2 or less, including the +3/+0 from O-Naginata's effect, as state-based actions are checked.
(wotc • 2020-08-07)
Rulings
O-Naginata can become attached to a creature only if that creature's power is 3 or greater before O-Naginata is attached to it.
(wotc • 2020-08-07)
O-Naginata's equip ability can target any creature you control—but if the creature's power is 2 or less, it won't become attached as it resolves.
(wotc • 2020-08-07)
O-Naginata becomes unattached if the equipped creature's power is reduced so that its power is 2 or less, including the +3/+0 from O-Naginata's effect, as state-based actions are checked.
(wotc • 2020-08-07)