Kamio Yui wa Kami wo Yui, Futari no Taisei Recommendations
Both have the same central concept of two characters (or personalities) sharing one body. The rules are mostly similar as well; only one character can occupy the body at a time and when one character emerges, the body undergoes cosmetic changes to distinguish them.
In Yui Kamio, the personalities are in stark contrast (violent vs. gentle) and a seal influences which character will be present. The change is shown through a palette swap of hair and clothes.
In Taisei, it is suggested that the two are twins who have merged together. One occupies the body at daytime while the other takes nighttime. Their change is represented by