Witch Queen of Transfiguration, Sinclair Ruling?

Witch Queen of Transfiguration, Sinclair

[Stride]-Stride Step-[Choose one or more cards with the sum of their grades being 3 or greater from your hand, and discard them] Stride this card on your (VC) from face down. 

[ACT](VC)1/Turn:[Counter Blast (1)] If you have a heart card with "Witch" in its card name, and the number of your opponent's grade 0 rear-guards is two or more, your opponent reveals ten cards from the top of his or her deck, chooses a grade 0 card from among them, rides it, shuffles his or her deck, until end of turn, that unit gets "[AUTO](VC):[Counter Blast (1)] At the beginning of the guard step of the battle that this unit was attacked, you may pay the cost. If you do, choose any number of cards from your hand, call them (GC) as [Rest]." and "[AUTO](VC):At the end of your opponent's turn, choose up to one card from your soul, and ride it.".

The question is Guardian ruling. So basically, normal guard requires to follow the normal rules such as in the text it says,

Guardian Call:
The opponent can Call Guardians from their hand to protect the Unit under attack. The opponent may play any number of cards from their hand to add their Shield power to the power of the unit under attack. The Shield power is found in the yellow square on the left side of the card. Some units have no Shield Power and cannot be called as Guardians. The Guardians must also have a grade equal to or lower than that of your Vanguard. Called Guardians should be placed in the Guardian Circle to keep track of the during the fight. There is no cost to Call Guardians, but all called Guardians will be retired to the Drop Zone at the end of the battle. 

The opponent may also use the 'Intercept' ability (specific to Grade 2). If you have a unit in a Rear-Guard Circle in the Front Row that has the Intercept ability, you may move them from there to the Guardian circle and their Shield will be added to your unit's power as well. Just like other Guardians, they will be retired to the Drop Zone after the battle. Units with Intercept can intercept even if they are Resting. You cannot Intercept with your Vanguard and thus having an Intercept icon gives no benefit to a Vanguard. 

So now, from Witch Queen of Transfiguration, Sinclair skill, it says, ..."[AUTO](VC):[Counter Blast (1)] At the beginning of the guard step of the battle that this unit was attacked, you may pay the cost. If you do, choose any number of cards from your hand, call them (GC) as [Rest]."

After few discussion in the group, the skill will be consider as Superior Call to Guardian circle. So, let's say you are using the skill, your opponent may still guard with any cards as long as he/she pays the cost. With Triple Drive at the late game the skill can be really overpowered, maybe that's why to put it that way to stable the skill.