Objectives: This study investigates the impact of M&L psychotherapy on an adolescent with anxiety disorders transitioning into adulthood, using a retrospective mixed-method approach. Methods: An adolescent with Diagnostic Statistical Manual of Mental Disorders (DSM)-5-diagnosed anxiety disorders underwent combined treatment with M&L psychotherapy and complex Korean medicine therapy over a period of approximately two years. Patient records tracked the diagnosis, treatments, and progress. In-depth interviews were also conducted. The study used a convergent parallel mixed-method approach, integrating quantitative analysis from psychological assessments, including the State-Trait Anxiety Inventory (STAI-X), the Core Seven Emotions Inventory-short form (CSEI-s), and the Minnesota Multiphasic Personality Inventory-2 (MMPI-2), with qualitative analyses of traditional Korean medicine counseling session notes, interviews, and other qualitative psychological assessments. Results: State anxiety decreased from 40 to 36, and trait anxiety decreased from 42 to 34. MMPI-2 L scale scores decreased slightly to 64T, whereas S scale scores increased to 62T, and FRS scores decreased to 70T from an initial score of 78T. Qualitative analysis revealed an increase in the MMPI-2 Es scale, identified as “subjectivity.” Joy (喜) emerged as the highest emotional profile score in the CSEI-S. Scores for anger (怒), thought (思), fear (恐), and fright (驚) decreased, indicating improved negative emotions. Qualitatively, expressions of determination to “move forward” and “strengthen the mind” were noted, suggesting enhanced “lower danjeon (下丹田).” Conclusions: Integrating traditional Korean medicine treatment with M&L psychotherapy for a vulnerable adolescent with anxiety disorders demonstrated efficacy. Further research is warranted to substantiate the effectiveness of M&L psychotherapy and advocate for its wider adoption in mainstream practice.