As many people are aware of, the removal of monsters by tributing them for Kaiju monsters, or "Kaijuing", is a relatively common way of dealing with threatening monsters that are hard to get rid of.

In this situation, Battle Butler has a relatively unique floating effect, however. A line in Prank-Kids Battle Butler's effect reads:

If this card in your possession is sent to your GY by your opponent's card: You can target 1 non-Fusion Monster in your GY; Special Summon it.

This line is odd, because instead of saying battle or card effect, it just says "card".

When I tribute a Battle Butler to summon Gameciel, the Sea Turtle Kaiju (or any other Kaiju), does it's floating effect activate? It has been tributed by a card in my hand, but now that it's summoned to the opponent's field, it's "their card".