noun, na-adjective, noun which may take the genitive case particle 'no'
freely; at will; as one pleases
Describes doing something with complete freedom and control, without restriction. Often used in literary or formal contexts.
彼は如意自在に筆を操る。
He wields the brush with complete freedom.
如意自在の境地に達する。
Reach a state of complete mastery.
自由自在 is more common and neutral, meaning 'freely' or 'at will'. 如意自在 is more literary and emphasizes acting exactly as one wishes, often with a nuance of mastery.
A yojijukugo (four-character compound) combining 如意 (as one wishes) and 自在 (freely, at will). The exact historical derivation is uncertain, but it likely originated from Buddhist or classical Chinese texts.