Undyne was admitted to UMH after a recent visit to another UMH resident, Alphys. Being good friends with Alphys meant that Undyne was in and out of the hospital quite often. However, as the visits went on Undyne became noticeably thinner and far more reserved. Eventually she'd become so thin that she looked like sheets of skin had been draped over a skeleton. That was when Toriel decided to keep her at UMH, where she was later diagnosed with Anorexia Nervosa.
Undyne is incredibly thin. She wears oversized tank tops and shorts, and tends to keep her hair down; however she will put it up on occasion.
Undyne is usually quiet, but can crack the occasional cynical joke. It's rare that she gets angry.
Undyne doesn't take a liking to Frisk when they first meet. She constantly threatens Frisk's life and, if not monitored carefully may actually attempt to harm her. However as time goes on, Undyne grows a soft side for Frisk after watching her talk with Papyrus and Alphys. This allows Frisk to gain Undyne's respect and become her friend.
Undyne refuses to speak to Frisk in the Neutral run. She feels Frisk's strange aura and, unsure of her intentions stays away.
In Genocide, Undyne is one of the patients Frisk has an easy time going after. Despite being enraged at Frisk's harm to Papyrus she can easily be knocked down if Frisk insults her appearance. If and When Frisk insults Undyne, said fish will go into solitude and not be seen again during the Genocide Story, only heard from (if she lives, that is) through Alphys.
W. D. Gaster
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