Kanda watched Allen as he ran back and forth trying to put together a costume. Lavi's family had a lot of old clothes so they went to his house to dress up for Halloween.
Why was Kanda there? He was "forced" to come because "Allen wanted him to see which costume suit him best". In reality Kanda wanted to see Allen being cute. Don't deny it Yuu Kanda we all know you do.
"Yuu! Does this look good?" Allen asked as he came out with a skull mask that was at the side of his head instead of on his face, black oversized Victorian clothes, a staff and a big witch hat.
Kanda wanted to laugh but he held it down, "Sure."
Allen pouted, "Is it scary?"
Kanda tapped his chin as if he was actually thinking about it, "You'll kill everyone once they see you in that." Since you're so cute not scary.
The younger child beamed, "Really!"
Kanda nodded, "Really."
Allen ran to the Bookman to tell him that he'd borrow the clothes he had on.
Lavi came from behind holding samurai clothes for Kanda, "Just don't rape him okay? You'll have to wait a few more years for it to be legal."
Kanda growled and tore the costume away from Lavi's grip, "Shut up."
That night…
Allen proceeded to kill everyone with his "scariness". The whole block had to be treated for nosebleeds, even the doctors themselves.
Kanda smirked as Allen told his parents how he was so "scary" that everyone collapsed from blood loss. One day he would tell Allen why they really did.