If this card is destroyed by your opponent's card (either by battle or by card effect), your opponent cannot Special Summon a monster, or activate Spells, Traps, Spell/Trap card effects, or Monster Card effects, for the rest of this turn.
How to Get
Activates from your Graveyard
Prevents activation of your opponent's Effect Monsters / Prevents activation of your opponent's Spell Cards / Prevents activation of your opponent's Trap Cards
I never play the game so I don't know the story, but based on their decklist, it seems the Duel Academy version of Rua and Ruka have a story where they accidentally have their deck swapped, resulting in Rua running Ruka's Watt deck and Ruka running Rua's Batteryman deck.
Basically, Ruka has a Watt deck in TF5, although she never gets to use it.