na-adjective
Describes something organized according to a clear system or method, often used for knowledge, study, or approaches.
彼は日本語を体系的に勉強している。
He is studying Japanese systematically.
この教科書はとても体系的でわかりやすい
This textbook is very systematic and easy to understand.
From 体系 (system) + 的 (-tic, adjectival suffix).