The phrase "to become a butterfly" is an idiomatic expression that means to undergo a transformation or metamorphosis, often in reference to personal growth and self-improvement. Full definition
Students will become butterfly scientists and learn about the body parts and life cycle of butterflies. (naturemuseum.org)
They also have an intern program that will teach you everything you need to know about becoming a butterfly farmer; how awesome is that? (temporaryprovisions.com)
After 10 months of freeloading, the caterpillars become butterflies and take off on their own. (discovermagazine.com)