“The second thing that I should tell you,” Clovis said. “Is that the only way to hurt a Stand is with another Stand.”

Silence filled the room. Suddenly, it made sense why Clovis would reveal that particular pair of facts. It was confirmation of something obvious. Lelouch stared at Painted Black. The shadow Stand shrugged, as if to say “Don’t ask me”. As it was, there was nothing he could do but confirm what Clovis had already figured out: His Stand couldn’t attack. Then again…

That first kick had struck the area where Painted Black had been, and Lelouch hadn’t felt anything at all. Could it be… His Stand could only interact with items by making them invisible… Which meant that even other Stands couldn’t hurt it! But by that same token, it couldn’t be used to hurt other Stands. The only weapon he had to attack was his gun. A gun with only four bullets left.

-Lulu's Bizarre Rebellion Chapter 3