Because I imagine there aren't that many Union Monsters here...

[Spenstar]

And Union monsters and Spell Counters don't seem to go together often, so...
 
 
 
LORE: Once per turn, during your Main Phase, you can equip this card to a monster you control that can use Spell Counters as an Equip Card, OR destroy the equipped monster and Special Summon it in face-up Attack Position. While equipped to a monster by this effect, place 3 Spell Counters on the equipped monster. If you cannot, place the remaining Spell Counter(s) on this card and transfer them from this card to the equipped monster when possible. If this equipped card is destroyed, remove all Spell Counters from the equipped monster. (A monster can only be equipped with 1 Union Monster at a time. If the equipped monster would be destroyed, this card is destroyed instead.)
 
Pretty sure the OCG could use some work, you can barely even see the card text!
 
Anyway, this card is meant to bolster cards that like Spell Counters. 3 because it's the magic number, but I can easily change it. If a monster only gets 1 counter, Spell Conjure will be a good set of extra hands and hold the other 2 until the monster needs it. So Breaker the Magical Warrior can use its effect 3 more times, Silent Magician Lv4 is that much closer to an upgrade, Skilled Dark Magician's all set, Dark Red Enchanter gets a boost, and so on. The limitation text is to prevent abuse. If the card is destroyed, you lose all your spell counters, so play wisely. And you can't detach it from Breaker, re-equip it the next turn, and have 3 more uses. If you do that, Breaker goes to the grave.
 
My skills/OCG is a bit rusty because I haven't played in a while and I'm still in a mid/late GX mindset. Synchro and Xyz mean nothing to me. Keep that in mind while rating.