"은/는" is not always a topic particle.
It is rather a particle that sets limits of meaning.
It can be used as :
- • 나는 과일은 먹었다. I ate fruits (for example, "but not anything else") (used as an object)
- • 그는 학교에는 갔다. He went to school (for example, "but anywhere else" or "depite illness") (used as a adverbe)