Micro Services architecture issue

I have a design which is based on an API gateway which calls several micro services. One of them is a rule manager which run different tests for a given request. The problem arises when this module needs to fetch data from different tables for each rule check. The caller (the API) is not aware of this module data needed to run the rules. On the other hand, it looks pretty awkward that this micro service will gather data from many other micro services in order to run. (The data spreads on many tables) What's the best practice for that?

Thanks