One of the constant recurring themes in the series is that of light and darkness. Rikka, Yuta and Sanae incorporate typical dark magic archetypes in their chunibiyo alter egos. It seems that darkness represents the internal desires one has and desperately craves, as opposed to the light which represents reality and the responsibilities one has to others. No other character represents this theme more than Rikka: her desires to withdraw into her chunibiyo phase and see her father again are played up against the responsibility she has towards her social and academic development. The series sets a rhythm by balancing these two needs: her fantasy is a protective escape mechanism for dealing with the heavy emotions of her father's death. While she doesn't completely outgrow them, she does make fantastic progress in the form of making friends, progressing in school and generally being open to more positive experiences.
Rikka's eyepatch and colored contact lens also represent her wish to deny the reality in front of her. This can be seen from her reality rejected activation every time a battle comes up. She does not wish to see the world in front of her in the way that is - she wants to go back to when her family was whole and happy. How she ended up in chunibiyo also represents this: she picked it up from Yuta (unbeknownst to him at the time) and used it to lead her mind off of the consecutive losses she's suffered.
