Fabled Unicore vs. Rivalry of Warlords

Let s say both player have the same amount of cards in their hand, so that unicore has its effect active.

Turnplayer:
Fabled Unicore + 1 face down Monster

Player2:
face up Rivalry of Warlords

Turnplayer flip summons his face down to face up.

Turnplayer:
Fabled Unicore (Beast) + Summoner Monk (Spellcaster)

Player2:
face up Rivalry of Warlords


Now:
What happens?
Rivalry tries to activate its effect.
Does Unicore negate and destroy it? Or is the effect of Rivalry permanent, and doesn t need to be activated?

Thx!

you cannot flip summon that monk.

moreover rivalry has continuous effect.