Kagami's "Getto daze", translated to "GET!", is a reference to Pokemon, specifically after catching one; Kagami uses it because she "caught" Konata. This is what prompts Konata's comment about the wrong game, since they're apparently costumed in Dragon Quest attire.
Kagamin, scary!! ...and that's the wrong game!!Auu...Hu hu hu hu hu hu hu hu hu laughterKona-tan, GET! "Getto daze", translated here to "GET!", is a reference to Pokemon.