Well I watched episode 5 of R2, I understand the tomato bit but the robot ears? At the beginning of the episode she has normal ears but then when she appears at the festival, CHACHAMARU MODE.
Well the in-universe reason is that it's just a disguise - a terrible one at that. The real life reason is that it's probably either a cute thing to do to her for fanservice reasons and/or it's a homage to a character. Chachamaru is just one of many anime girls to have those robot ears.
