Each time a Spell Card is activated, place 1 Spell Counter on this card when that Spell Card resolves. If a card with a Spell Counter(s) is destroyed, place its Spell Counters on this card. Once per turn, if you would activate a card effect by removing a Spell Counter(s) from your side of the field, you can remove that many Spell Counters from this card instead. If this card would be destroyed, you can remove 1 Spell Counter from this card instead.
Master Magician can be special summoned from your hand/graveyard using Citadel's spell counter. While building up the 6 counters can be somewhat slow, this can be used to revive Master Magician in a prolonged duel.
Once per turn, you can increase the Citadel's spell counter using this trap card. Can be a more guaranteed way to increase the number, but also useful if you use other monsters that can benefit from spell counters.
Red Magician's effect can be used in the graveyard to add a spell counter. Beneficial if you use the field spell together with monsters that can benefit from spell counters.
Spellbooks are easily able to search each other fetch each other especially with Spellbook of Secrets, Spellbook of Power, Spellbook of Eternity, and Spellbook of the Master, making them an ideal way to quickly gain counters without losing advantage.