Kafka produce a new event when all previous event are consumed

Question

In our system, we would like to create a new event based on other topics data. Scenario: we have 3 topics that contains useful data for create a user for example. To create the user we need to have all the data from those 3 topics and the create a new events with all or some part of those data.

I don't like the idea to merge topics so I assumed that the best way is to store data from 3 topics and every time we save them we need to check if we have all data for a consistent user model. We will have a database to store this data and when the user is valid we can generate a new event with its data.

Do I have other options? I would like to avoid merge topics or sagas.