Is there a way to have an intermediate observable independently output values in an observable chain?

For example:

val obs = BehaviorSubject.createDefault("a")

BehaviorSubject.createDefault(0)
    .flatMap {
        obs
    }.subscribe {
        print(it)
    }

obs.onNext("b")

The result of the above is:

a

but I'd like for there to be some sort of operator that allows for obs to independently output values within that same observable chain so that the result would become:

a
b

Is there some operator that allows for that?