A character who is sympathetic with a main character, thus revealing the main character's thoughts, is

- Confidant character.

Explanation:

Characters play a vital role in solving the author's purpose and conveying the intended idea, message, lesson, or impact, that the author intends to convey or create.

'Confidant Character' is demonstrated as the character within whom the central character or protagonist divulges. However, such a character does not require to be a person but it can rather be an animal or another anonymous being with whom the trust of the main characters lie (as an authority figure whom the major character confides in) and discloses his/her deepest thoughts. Such characters are employed as secondary characters who function to drive the narrative forward by disclosing the true thoughts, intentions, or personality of the central character that indicates the upcoming action or events.