Undyne the Undying vs Bete Noire (Battle)

After Gaster's defeat, Alphys evacuated Jessica and Gaster because she had a plan.

However, it failed because the weapon was supposed to only work on humans and monsters, and Bete is neither of the two.

Undyne accidentally killed Alphys and got brutally speared until her determination saves her. This Battle involved Undyne and Bete.

Context
While Asgore, Asriel, and Frisk were fighting in the school, Undyne may have helped the local police to fight the pink creatures in order to protect the civilians.

Jessica and Gaster were returning from the plan's failure and Papyrus was healing Gaster.

Undyne asked for knowing what happened to Alphys, she runs in vain to save her life and kills her by Bete's mental manipulation.

Undyne was easily defeated until her Determination saves her life.

Battle
In the first phase of the battle, Undyne easily assaulted and hurt Bete with everything that her Determination allows her to do, which resulted in Undyne having the upper hand and was nearly able to kill Bete, even if she used her new weapon "Rhabdophobia". In the second and final phase of the battle, Akumu decided to eat the HATE Vial. The HATE acted as an enhancer and saved Bete from possible death in the exchange of her mental sanity.

Later, Bete retreated because the HATE was taking over her body. Undyne fell to the ground by exhaustion and cries after remembering that she killed her girlfriend. She then goes back to the house.