Erika was a fair-skinned girl with long dark-blonde hair that is tied in a lateral ponytail and her eyes are a mixture of yellow and green.
Erika was also mentally ill shown when she watched as a senior named Shota Arai tries to rape Aya, but Aya escaped so she and Shota looked for her.
Erika was also sadistic as she mocked Aya about the cat that she cared for by saying "The guts went everywhere." before throwing the collar to Aya, which triggered Aya to use her Stick and indirectly killing her and Shota.
Erika was also a delinquent, which is further proof of this is when one student said "Both of them were delinquents anyway, so aren't they better off dead?" who was often rather pleased that Shota and Erika are dead.
- The name Erika is written in hiragana (えりか), which has no special meaning.
- Erika's surname Kaijima means "shellfish" (貝) (kai) and "island" (島) (shima/jima).
- In the manga her surname was sometimes mistakenly referred to as Kajima.
- In both anime and manga, it is shown that Erika and Shota Arai are the first two people to get used a stick on by Aya Asagiri.
- Shota's and Erika's deaths were also the first to be seen in the anime and manga.
- She, Alice, Melissa, Louise, Ray and May are the only known characters to have first names that aren't Japanese as their first names are common in the American and Europe continent.
- Erika is an English and Italian name with Nordic and German origins.
- Judging by her name and the color of her hair, Erika probably was Half-Japanese (by her father's side) and Half-American (by her mother's side).
- This is because the Japanese have to have a Japanese parent and a foreign parent to be blond.
- In the Episode 1, some of the students who delighted with the shadow of the accidental death of Erika and Shota and laughed away spreading unfounded rumors such as heart and triangle relations were fun.
- Erika's death was the reason that Sarina Shizukume's hatred for Aya Asagiri grew, though Sarina's hatred didn't last long, her death was also one of the reasons why Sarina became a Magical Girl.
- Her parents have never been seen or mentioned, but they will surely have been devastated by their daughter's death.
- It is implied that the Kaijima spouses were not acquainted of their daughter's cruel and sadistic nature.
- Due to the fact that she killed a cat, it is implied that if Erika had never died, she would become a serial killer as an adult.
- In the Chapter 137, It has been shown that due to the fact that Aya has gone back in time by saving the herself of the past to prevent her from becoming a magical girl, she have never used her stick.