na-adjective
Describes a mutual or two-way relationship, action, or effect. Often used in formal or technical contexts.
両国の関係は相反的であるべきだ。
The relationship between the two countries should be reciprocal.
この契約には相反的な義務が
This contract includes reciprocal obligations.
Compound of 相反 (sōhan, 'reciprocal, opposite') + 的 (-teki, '-like, -al'). The base 相反 is itself a Sino-Japanese compound of 相 (mutual) and 反 (opposite).