1. A method for at least one of characterizing, diagnosing, and treating a mental disorder, associated with microbiome functional features, in at least a subject with the mental disorder, the method comprising: for each of an aggregate set of samples, from a population of subjects determining a microorganism nucleic acid sequence, comprising: identifying primers for nucleic acid sequences associated with the microbiome functional features associated with the mental disorder, fragmenting nucleic acid material from the biological sample, and amplifying the fragmented nucleic acid material using the identified primers; and determining an alignment of the microorganism nucleic acid sequence to a reference nucleic acid sequence associated with the microbiome functional features associated with the mental disorder; generating a microbiome functional diversity dataset based upon the alignment; receiving a supplementary dataset informative of presence of the mental disorder within the population of subjects; extracting a set of functional features from the microbiome functional diversity dataset; transforming the supplementary dataset and the set of functional features into a characterization model of the mental disorder; and identifying at least a subset of the set of functional features associated with the mental disorder, upon processing a sample from the subject with the characterization model, thereby generating a diagnosis of the subject with the mental disorder based upon the set of functional features; and providing a therapy to the subject with the mental disorder based upon the diagnosis, wherein the therapy modulates microbiome functional diversity to alleviate the mental disorder.