Word/phrase for describing a relationship/association that could be productive and conterproductive

Question

How to explain such a relationship/association (preferably not in the human context) :

Approach A could be regarded as an innovative idea to leverage full potential of system B. In the reverse direction, it's possible to leverage concept A to attack to the system B.

Based on the answers of a similar question, such feature may be referred as double-edged sword or mixed blessing. Now, how can we refer to the relationship/association shaped around this feature?

I think "A and B have a double-edged sword like relationship" makes no sense. So, there is need to another word/phrase or even an idiom to describe that.

Answer 1

The relationship between A and B cuts both ways

cut both ways - Having a mixed effect, to have advantages and disadvantages; to have two different effects at the same time, usually one good and one bad; To have both favorable and unfavorable results or implications; to affect both sides of an issue equally; to work both ways

e.g. The Internet cuts both ways – it not only opens borders, it draws boundaries between the people who have it and those who do not.

You could also say (as @Graffito did), "A and B are ambivalent toward one another"

Ambivalent - Having mixed feelings or contradictory ideas about something or someone

Citations from the Oxford Dictionary and The Free Dictionary Idioms

Answer 2

In this case A is the double edged sword. B is the context in which A is double edged. I don't see humans as entering into it.

As far as B is concerned, A is a double edged sword.

would be one way to put it.