Karen is admired by other students due to her calm and stoic nature. This, however, is her outer character—she is actually very lonely, especially when thinking about her parents, whom she secretly misses. Because she has known Komachi for such a long time, Karen often feels responsible for being there for her; to an extent, she feels this way about everyone, believing it to be a natural responsibility of the president of the student council. Because of her position, Karen is able to memorize all the names and faces of all the Cinq Lumières students, and also easily takes responsibility when something happens to the school, as seen in the second episode where she wants Nozomi to explain what happened to the library the other day.
Aqua Stream - Cure Aqua spines around herself once while chanting, and reaches her right hand upward, and the hand begins to glow blue. A stream of water then begins to spiral around the screen before Cure Aqua thrusts her palm towards the enemy, making all the water flow to the Kowaina to purify it.
Aqua Tornado - Cure Aqua's butterfly bow begins to glow, in which the light reaches out toward her left hand. The Aqua Ribbon is then shown, in which she takes it over to her right hand. She then spins around herself once while chanting, and the Aqua Ribbon begins to emit a stream of water that spirals around the screen before Aqua thrusts the Aqua Ribbon at the enemy, making all the water flow at the Kowaina to purify it.
Sapphire Arrow - Cure Aqua makes first with both hands and crosses them in front of her chest, causing the butterfly emblem to glow in her signature color. Tiny droplets of water then begin to swirl around her. She reaches forward and her hand becomes surrounded in a tiny mist. The water gathers into an almost solid form which Aqua grabs a hold of and bends back into the shape of an archery bow. A large, drill-like torrent then rips from the bow. When the arrow hits, a blue butterfly appears, purifying the Hoshina.
- Cure Aqua is the first blue cure in Pretty Cure history, followed by Cure Berry, Cure Marine, Cure Beat and Cure Beauty.
- Cure Aqua is the first Aquatic-themed cure in Pretty Cure History, followed by Cure Marine & Cure Beauty.
- Karen occasionally shows an exaggerated fondness for grape juice.
- Karen has a number of similarities to Honoka from Futari wa Pretty Cure, most notably their nearly identical backgrounds and their reputations for being highly intelligent and polite. As such, her relationship with Rin is interesting in how much it differs from Honoka's relationship with Nagisa. This may be due to their opposite Cure forms; Cure Rouge and Cure Aqua control fire and water respectively, which are frequently depicted as opposites. Also, as Urara points out in the same episode, the two also represent passion and intelligence, another well-established opposite.
- Karen's relationship with Milk is implied to be analogous to those between Nozomi and Coco (Koji Kokoda), Komachi and Natts, and Urara and Syrup.
- Karen is never seen expressing romantic interest in a male character, except when others are doing the same.
- Cure Aqua's Aqua Ribbon is the source of a rare inconsistency between the animation and merchandise. Merchandise representing the item consistently depicts it as a long, blue, whip-like ribbon attached to a handle similar in appearance to the Rouge Tact. In the animation, however, the ribbon is absent; the item consists solely of the handle, which the writers would occasionally interpret as a sword hilt. The reason for this discrepancy is unknown.
- Cure Aqua, along with Cure Marine and Cure Beauty, differ from the other blue Cures in the series as their hairstyle in their transformed state is not a purple ponytail. Cure Aqua instead has a blue ponytail.
- In the Pretty Cure All Stars Suite Flower Card Collection, Karen is represented by the iris, which symbolizes love and sympathy in the Language of Flowers.
- Karen is the first cure in Pretty Cure history to play a musical instrument (violin) the other one being Hibiki Hojo (piano) and Ellen Kurokawa (guitar).
- Karen is the first Cure to have a butler, followed by Alice Yotsuba.
- Her pose in Pretty Cure All Stars New Stage 3: Eien No Tomodachi, it resembles Cure Mint's pose.
- Karen will appear as Cure Aqua to give the 10th Anniversary Congratulatory Message at the beginning of episode 7 of Happiness Charge Pretty Cure!
- Karen and Hibari Kyoya from Reborn, which is both a position as Student President.