Seven Day Alternating Personality Syndrome (Web Comic)

Girl(?) has a disorder that causes her(?) to switch into one personality for every day of the week. Follow each personality as it tries to understand what's happening around them, and what happened since they last appeared. Throw in a mysterious costumed figure in the background, and you get this series.

May or may not be updated since the cancellation of the serialized version.
Also available on NicoNico Seiga https://seiga.nicovideo.jp/comic/39301