Background: Tirzepatide, a glucose-dependent insulinotropic polypeptide/glucagon-like peptide-1 (GLP-1) receptor agonist, has recently been introduced in Japan; however, there are limited studies on its effectiveness in Japanese patients with type 2 diabetes diagnosed with metabolic dysfunction-associated steatotic liver disease (MASLD). This evidence concerns the gene GIP and type 2 diabetes mellitus.