Akuma no Oni (experienced 2) Shadowlands • Nonhuman • Oni • Overlord • Experienced 2 Oni no Akuma • Unique After Akuma enters play: Lose 15 Honor and destroy your rightmost province. During the Action Phase, Akuma does not bow and may not be targeted. Once per game, after a battle's resolution in which an attacking army containing Akuma destroyed a province: Destroy another of the Defender’s Provinces.
Unexpected Arrival Battle: If any enemy units are at the current battlefield: Target a Personality in one of your provinces. Bring him into play at the current battlefield, paying 2 less Gold and ignoring his Honor Requirement.
Decree of Peace Until your next turn begins, after a player destroys a province as the Attacker, the Empress exacts retribution for defying her reign; destroy that player's leftmost province.
If a player who has Akuma no Oni xp2 in one of their provinces while Decree of Peace is in effect, would using Unexpected Arrival to bring Akuma into play as the attack trigger the event's province destruction due to Akuma's province-destruction cost occuring while "as an Attacker"? I note that Decree of Peace has substantially different text than all similar cards -- it does not in any way refer to battle resolution (as Akuma's other trait) or to "winning a battle" (as Ring of Earth and Bayushi Sihaken).
Although Path of the Destoyer cards are not yet eligible for rulings, an extremely similar situation can occur with Bayushi Hisoka xp in place of Akuma no Oni xp2, although in that case, the destroyed province can be the Defender's.
All of this is very unlikely, admittedly, but Unexpected Arrival is the sort of thing that I like to poke at to see what shakes loose from the rules tree.