I hope Rica is exaggerating, because considering Takeshi as main character but not Koharu seems very bad news to me. Still, she also didn't count TR as main characters, yet we promised more active roles for them. So, Koharu might still be a very active part of the episodes, and might be developed further in future.
I guess Rica see main characters as the members of the main group. Not so much that the characters are so active.
It's pretty clear Ash and Go are traveling together in this season.
Koharu may have an active role, but she isn't a companion.