We are named Dark Guardians right? So the name itself it is already an oxymoron. "Dark" has a negative connotation, but "Guardians" is more positive.So then the motto should somehow explain the guild name, but yet give us an identity.
Hence, "Overshadow" fits "Dark", while "Outshine" fits "Guardians". When put together, it simply means that in order to stand out and maintain our presence, we need to rise above others.'''