Doitsu

Level 4 EARTH/Fairy Union Effect Monster
100 ATK / 200 DEF

Once per turn, you can equip this card to a "Soitsu" you control, OR unequip it to Special Summon this card in face-up Attack Position. When equipped to a monster by this card's effect, that monster gains 2500 ATK. (A monster can only be equipped with 1 Union Monster at a time. If the equipped monster would be destroyed by battle, destroy this card instead.)

Rulings – Yugipedia

Printings:

Cybernetic Revolution: CRV-EN025 (Common) - 2005-08-17
Dark Revelation Volume 4: DR04-EN025 (Common) - 2007-11-14

Prices:

Cardmarket: 0.07 €
TCGplayer: $ 0.12