1 mutual

1 to interact

2 interactive

1 each other

2 mutually

3 mutual

1 to follow each other's accounts (on Weibo etc)

1 interconnected

1 to compete with (idiom) (Tw)

2 to pit oneself against

1 mutually related karma (idiom); fates are intertwined

2 interdependent

1 mutually shirking responsibilities (idiom); each blaming the other

2 passing the buck to and fro

3 each trying to unload responsibilities onto the other

1 to confide in each other (idiom)

1 mutual exchange of assistance (idiom)

2 to benefit from each other's strengths and make up each other's shortfalls

3 to reciprocate with material assistance

4 scratch each other's back