noun-modifying (irregular)
Prenominal modifier meaning 'that is to come' or 'expected in the near future'. Often used in formal or written contexts to refer to upcoming events, eras, or people.
来るべき選挙に備えて準備を進めている。
We are making preparations for the coming election.
来るべき時代の変化を見据えた政策
We need policies that anticipate the coming changes of the era.
来る is the basic verb 'to come'. 来るべき uses the classical attributive form 来る (きたる) and adds べき to express 'should come' or 'expected to come'.
From the classical attributive form 来る (きたる) of the verb 来 (く) 'to come', combined with the auxiliary べき (beki) indicating expectation or obligation. The form 来たるべき explicitly includes the okurigana たる.