We have Dissociative Identity Disorder and are plural (https://morethanone.info). We also tend to use plural first-person pronouns (such as "we" or "us") to refer to ourselves as a system.
[ my public key: https://keybase.io/logandark; my proof: https://keybase.io/logandark/sigs/m6zjqnGMWscZConP_8q5dTxchLtZC37IPnwlaj0mBGo ]