self-contained; self-absorbed
Describes a person, system, or work that is complete in itself, not relying on or engaging with external elements. The 'self-absorbed' nuance applies when referring to a person who is wrapped up in their own world.
His novel has a self-contained worldview.
She is self-absorbed and doesn't listen much to others' opinions.
自己中心的 means 'self-centered' or 'egocentric', focusing on selfishness, while 自己完結的 emphasizes being complete in oneself, which can be neutral or positive.
完結的 means 'conclusive' or 'complete', but lacks the 'self' aspect; 自己完結的 specifically means self-contained.
Compound of 自己 (self) + 完結 (completion) + 的 (-like, -ish). The exact origin is uncertain, but it follows a common pattern for forming adjectival nouns.