What costumes you have cast/characters:

Also I'm sorry I'm not allowed to watch a lot of TV so a lot are boy/girl duos but you can pretend it's maybe a genderbend version or just dress up as opposite gender :)
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Louis:
Jim and Pam

Klaus:
Romeo and Juliet

Malina:
Squiward and Spongebob
(they deserve just as much attention as Patrick and Spongebob don't lie)

Violet:
Rose and Jack (either actually dress as Jack, or genderbend it.)

Dylan:
Spongebob and Patrick

Duncan:
Dustin and Steve

Quigley:
Dora and Diego

Isadora:
Anne and Gilbert (she's Anne, you can either be Gilbert or like a genderbend version/Diana.)

Avi:
Eleven and Max

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Not all the costumes are romantic, but they're matching still.