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, so it would be easier to manipulate others. That said, as stated by Hachiman in Season 3, she isn't by any means as bad as he thought, and despite her cuteness seemingly being an act and a bit mischievous at the beginning, Iroha genuinely is a good person at heart. With her development, she becomes less mischievous