If only this card is in the battle area and I use its ＜Start Your Main＞ effect to digivolve, is the digivolution cost reduced by 1?

Yes, the digivolution cost is reduced by 1.

What order do an effect that triggers when a card is removed from a security stack and a ＜Security＞ effect on a checked card activate when they trigger simultaneously upon a security check?

The ＜Security＞ effect will activate first. Upon a security check, a ＜Security＞ effect will immediately activate without pending activation.

Takuya Kanbara rulings (BT21-082)

2 official rulings from Bandai, last ruled Apr 4, 2025. Straight answers to how this card actually resolves.

Effect: [Security] Play this card without paying the cost. [Start of Your Main Phase] 1 of your Digimon or Tamers may digivolve into a Digimon card with the [Hybrid] or [Hero] trait in the hand. For each of your red Tamers with different names, reduce this effect's digivolution cost by 1.
Inherited effect: [Your Turn] [Once Per Turn] When your opponent's security stack is removed from, you may play 1 red Tamer card from your hand without paying the cost.

Official Q&A

If only this card is in the battle area and I use its ＜Start Your Main＞ effect to digivolve, is the digivolution cost reduced by 1?
Yes, the digivolution cost is reduced by 1.
Ruled Apr 4, 2025
What order do an effect that triggers when a card is removed from a security stack and a ＜Security＞ effect on a checked card activate when they trigger simultaneously upon a security check?
The ＜Security＞ effect will activate first. Upon a security check, a ＜Security＞ effect will immediately activate without pending activation.
Ruled Apr 4, 2025

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Questions and answers are Bandai's official rulings, collected and translated by the DigimonCardGame Wiki community and reused here under CC BY-SA. Card names and card text are © their respective publishers; Combalo is not affiliated with Bandai.

Takuya Kanbara rulings (BT21-082)

2 official rulings from Bandai, last ruled Apr 4, 2025. Straight answers to how this card actually resolves.

Effect: [Security] Play this card without paying the cost. [Start of Your Main Phase] 1 of your Digimon or Tamers may digivolve into a Digimon card with the [Hybrid] or [Hero] trait in the hand. For each of your red Tamers with different names, reduce this effect's digivolution cost by 1.
Inherited effect: [Your Turn] [Once Per Turn] When your opponent's security stack is removed from, you may play 1 red Tamer card from your hand without paying the cost.

Official Q&A

If only this card is in the battle area and I use its ＜Start Your Main＞ effect to digivolve, is the digivolution cost reduced by 1?
Yes, the digivolution cost is reduced by 1.
Ruled Apr 4, 2025
What order do an effect that triggers when a card is removed from a security stack and a ＜Security＞ effect on a checked card activate when they trigger simultaneously upon a security check?
The ＜Security＞ effect will activate first. Upon a security check, a ＜Security＞ effect will immediately activate without pending activation.
Ruled Apr 4, 2025

Got a line that uses Takuya Kanbara? Map it in the builder and share it with a link.