I studied pharmacology as an undergraduate and would like to answer your question.
Mirogabalin belongs to BCS class 1 due to its high solubility and membrane permeability.
According to the pharmacological specifications for TARLIGE TABLETS written in Japanese, milogabalin besilate is soluble in methanol, ethanol, and water. It also undergoes membrane transport via amino acid transporters, which is thought to be the origin of its relatively high permeability.
Other physicochemical properties include its melting point of 169°C and it does not appear to be hygroscopicity.