By definition a literary foil is "a person or thing that makes another seem better by contrast." So if Chase is Kimiko's foil, that would mean that he makes her seem better by contrast. Let's see what the two have in common then!

Chase has an older brother, known only as Monk Eon, who successfully bonded with Chase's crush, the dragon lady Loniani-Nui. Chase was also envious of Eon because his brother reached the level of Xiaolin Dragon Warrior before he, himself, did. Chase didn't want to give up a portion of his meager power, and that is the main reason why he was being held back and unable to advance to his brother's level.

While the two are never shown together prior to the series finale, one can deduce that Chase and Eon were often, if not always, together. Especially since they were both training under Dashi to reach the same goal of becoming a Xiaolin Dragon Warrior. After Eon reached the level of Dragon, Chase's resentment and jealousy must have only grown stronger because of how often he saw his unrequited crush and brother walking around.

In the finale, "Ride the Dragon!" Eon pleads with Chase to stop trying to destroy the world. Chase doesn't need to reshape things to get what he wants. Even Loniani-Nui's spirit is there to try and persuade Chase, but both fail and get absorbed. I'm guessing all the Chi spirits that were absorbed got returned to their bottles in the Yin-Yang World after Chase was obliterated by Tai Shui and the Cosmic Eye, and these two are safe and resting again. Chase, however is either dead or trapped between dimensions. The ending is unclear and ominous thanks to Tai Shui's quote of "Chase Young... not today and not in this way."

Chase refused to change his negative feelings and bad behavior and met his end as a result. Let's see how Kimiko compares.

Kimiko has an older sister, Tomoko "Tigress" Tohomiko. Unbeknownst to Kimiko, her older sister is a secret, multi-dimensional spy that prevents Aliens from invading Earth on the daily. Because Tomoko is seldom around due to her job, Kimiko treasured the time she got to spend with her older sister all the more! It wasn't until Tomoko missed Kimiko's fifth or sixth birthday due to being swarmed by a hoard of aliens that Kimiko began to resent her older sister. Kimiko assumed that her sister didn't care about her, and that's why she was hardly around.

After that, Kimiko believed that Tomoko might come back if there was a big accomplishment to celebrate--like joining the Xiaolin Temple--but Tomoko didn't even show up for that. Kimiko feels that, no matter what she does or accomplishes, it will never be enough to make Tomoko come back and share in Kimiko's pride.

However, that somewhat changes in "Tigress Woo," when Tomoko finally reveals what her job is to Kimiko. While Kimiko explains her feelings to Tomoko and pleads with her to stay, Kimiko knows she can't keep Tomoko with her forever. In the form of a truce, Tomoko gives Kimiko a way to stay connected to her, despite all the inter-dimensional travel the elder does. In spite of the ups and downs of that episode, Kimiko comes out of it understanding that, no matter what she thinks, Tomoko really does love her and wants to be there for her, but she can't right now. And... maybe that's okay. It doesn't make Tomoko any less proud of what Kimiko has accomplished or will accomplish in the future.

And Kimiko not only became a Xiaolin Dragon Warrior, but she is the first to ascend out of her generation of Xiaolin Monks! She even manages to defeat Chase in a one-on-one and save Dojo from dying of heat stroke (or boiling away; XC is weird that way).

Overall Kimiko has met great success in the face of many challenges.

In short, both Kimiko and Chase have older siblings that are more accomplished than them that they resent. Both feel unaccomplished by comparison to these older siblings, despite both respectively accomplishing quite a lot. And both have tried to resolve things by talking to their older siblings, often pleading for a change to happen. Across the board Kimiko is showcased more positively because she not only patches things up with her sister, where Chase was unable to set his feelings aside and resolve things with his brother, but Kimiko also becomes the first Monk in her generation to ascend--a feat that Chase didn't even accomplish in all his years.

So Chase is definitely an adequate foil to Kimiko. Where he missteped or was unwilling to change, Kimiko has succeeded and made accommodations. I feel that Shadow is the stronger written foil of the series, since there is a lot of lore to get out of how her relationship is written compared to Omi, but this post isn't about them. Comparatively all this stuff between Kimiko and Chase is very surface level and doesn't go very deep.

It would be interesting to put Kimiko and Chase alone in a room together and force them to talk about their emotions surrounding what I have discussed above in regards to older siblings. XC rather down plays it, but a large part of Kimiko's personality is that she has a (literally) firey rage. Chase himself has a lot of wrath and rancor bottled up. It would be at the whim of the writer if anything shippy were to come out of such a scenario, but at the very least it would lead to a lot of surprising personal development for both characters.

TL;DR

THE ANGRY KIDS NEED TO TALK ABOUT THEIR CRAPPY OLDER SIBLINGS WITH EACH OTHER!! >:UUUUU UUUUUU:<

Chase is a foil to Kimiko. His inability to set his feelings aside for the greater good sets up Kimiko as a stronger example of someone who is willing to do what's right to make a change by comparison.

There is a big difference between practicing re-draw, and stealing art in such a horrible way.

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