Hello, I was wondering if someone could verify if what happens in the following scenario is correct involving these two cards (this was tested in AI mode):

Number 38: Hope Harbinger Dragon Titanic Galaxy

Once per turn, during either player's turn, when a Spell Card or effect is activated on the field: You can negate that effect, and if you do, attach that card to this card as Xyz Material. When an opponent's monster declares an attack: You can detach 1 Xyz Material from this card; change the attack target to this card and perform damage calculation. If a face-up Xyz Monster(s) you control is destroyed by battle or card effect: You can target 1 face-up Xyz Monster you control; it gains ATK equal to 1 of those destroyed monster's original ATK.

Domain of the True Monarchs

While you have no cards in your Extra Deck and you are the only player that controls a Tribute Summoned monster, your opponent cannot Special Summon monsters from the Extra Deck. If a Tribute Summoned monster you control attacks an opponent's monster, it gains 800 ATK during damage calculation only. Once per turn: You can reduce the Level of 1 monster with 2800 ATK and 1000 DEF in your hand by 2 until the end of this turn (even after they are Summoned/Set, and even if this card leaves the field).

Opponent's Tribute Summoned Monster attacks Titanic Galaxy.

Titanic Galaxy prompts to redirect attack towards self (even though already attacked) then proceed to perform damage calculation.

When performing damage calculation, Opponent's Tribute Summoned Monster does NOT gain 800 ATK from Domain.

Is what occurs here correct?

Yes, its correct because Number 38 forces damage calculation. You can read that in the wiki.

http://yugioh.wikia.com/...er_Dragon_Titanic_Galaxy 

Yes, its correct because Number 38 forces damage calculation. You can read that in the wiki.

http://yugioh.wikia.com/...er_Dragon_Titanic_Galaxy 

Thanks, I just wanted to make sure since Tips are not always sure rulings.

Is there an explanation why this is so because I've found few cards that have the same wording of "perform damage calculation" and Damage Step rulings are always shady. Thanks!

Yes, its correct because Number 38 forces damage calculation. You can read that in the wiki.

http://yugioh.wikia.com/...er_Dragon_Titanic_Galaxy 

Unlike those cards' effects, "Domain of the True Monarchs"' 2nd effect is a continuous effect which doesn't create a chain link. It should apply even if the damage calculation is done by a card effect.

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