Iroha acts like an air-head or "clumsy girl" in front of most people to maintain her “cute appearance”. She maintains her image of an innocent girl in order to make everyone like her and make it easier to manipulate others.
In reality, she is much smarter than she lets on, and rarely shows her sly and calculating personality to others. Hachiman Hikigaya and Hayato Hayama see through her facade while others remain clueless.
As pointed out by Hayato, she worries about her public image. She didn't want to lose the student council election in a way that would make her look bad. Although she has no issue with being seen around Hachiman who is "hated" in the school.
According to Hachiman's observations, Iroha is an uncute Komachi Hikigaya, better Minami Sagami, phony Meguri Shiromeguri, different Kaori Orimoto and inferior Haruno Yukinoshita. He later deems her the "the second most rotten person in the world", the first obviously being himself. Hachiman feels that she is the type to be hated by other girls for her cuteness and her closeness to Hayama.
She lacks self-confidence but this starts to change when she overhears Hachiman's request for "something genuine". And after the Christmas play is completed successfully.
