I know that this a common expression in English but it doesn't really make grammatical sense. In English, you usually must put a subject before the verb to indicate who is performing the verb. The sentence should be "I will see you" or "We will see you." or "We will see each other." The only time you can use a verb without a subject is if it is a command. For example, someone might say, "Study!", "Drive!" or "Look!". If you take this sentence literally, then without a subject before it, the sentence is actually a command. You are telling a person to see themselves. However, for some reason the verb "see" is not used as a command in English. We usually say "Look!" if we mean it as a command but I suppose that saying "See!" is unusual but not technically wrong.