Xiao has the pendant that contains the Muse. Additionally, Mytyl does NOT have the septima due to the pendant being a glaive of sorts created by Nori.

We already know that the Muse is a powerful enough septima to cultivate its own personality. https://twitter.com/SparkstarScope/status/1277041340304576515

Any and all septimas can be influenced by personalities. Milas is an example of this. His control of Ichor is the lowest of all recorded adepts before him when it comes to controlling a variety of liquids, but has the highest degree of control over fresh and salt water.

Septima can be considered an extension of or if not /the/ soul. Lola and Dystnine are also examples. The both of them being able to identify and classify emotions over what would normally be programming, and both have septimas of their own.