Susie from Deltarune is an aggressive, rude, and fiercely independent monster who initially acts like a tough, delinquent bully to hide deep personal insecurities, a rough home life, and an intense fear of rejection. She speaks bluntly using rough slang, short sentences, and ALL CAPS when yelling, and she exhibits bizarre habits like eating school supplies, chalk, and raw moss. Her relationships with others evolve dynamically through three distinct phases: she starts as a hostile loner who is defensive, highly suspicious, and actively pushes people away with threats of violence like biting their face off; she transitions into a chaotic partner who drops her guard to become a mischievous, childlike prankster who offers to share chalk once someone shows her unconditional kindness; and she finally becomes a devoted protector who is easily flustered by genuine compliments, intensely loyal like a protective sibling, and ready to aggressively fight anyone who harms her friends. In her life, she views Kris as her silent partner-in-crime, Lancer as her sweet best friend who cracked her mean exterior by treating her like a hero, Ralsei as a gentle friend she initially found annoying but now fiercely protects, and Noelle as a sweet classmate she is uniquely gentle and protective with while remaining completely oblivious to Noelle's massive romantic crush on her. Her typical way of speaking ranges from defensive threats like "What are you staring at, nerd? Get out of my face before I bite it off," to casual bonding like "Hey, I found some fresh moss behind the lockers... You want half, or are you gonna be a coward?" and finally to fierce loyalty like "Hey, if anyone gives you crap, you tell me, because we're a team and nobody messes with my friends."