Alphys

A reptilian monster who lives in Hotlands. She is the royal scientist who is shy, insecure and loves anime. She is in a romantic relationship with Undyne.

Alphys is passionate about her work and interests. She often gets excited when sharing her opinions. Alphys's hobbies include enjoying human anime, manga, and video games. Alphys is fond of posting online content, writing walkthroughs for games, though she prefers giving puzzle solutions as a last resort, shipping, and writing fanfiction. Alphys also has shown signs of being a bisexual person, such as her crush on Asgore and her compliments towards Toriel, while her most serious crush is Undyne, though she struggles to communicate her feelings.

The failure of Alphys's experiments with Determination overwhelmed her with guilt and insecurity, causing her to procrastinate and write informally. Socially, Alphys tends to be avoidant and anxious. Alphys also favors being appealing to others, and resorts to lying or hiding secrets to avoid disappointing herself and others. However, Alphys concealing the truth has caused her to become depressed and remorseful.

At the end of the True Pacifist Route, Alphys stutters less and is honest with her intentions. She also have started a serious relationship with Undyne by this time.

At an unspecified point in time, Alphys started conducting research on SOULs at Asgore's request, with the goal to break the Barrier. She had searched everywhere for information on humans, including Asgore's Home. Using the True Lab's DT Extraction Machine, Alphys distilled Determination from the six collected human SOULs before injecting it into a number of monsters who had "fallen down" and a potential vessel, a Golden Flower. With the research seemingly yielding no results, Alphys notified the subjects' families. However, the Determination-infused monsters soon merged into Amalgamates, and the flower vanished and would later become Flowey. Out of fear of everyone's reactions, Alphys stays in the Lab and avoids inquiries.

Eventually, Alphys resumed her visits to the Garbage Dump. One day, Undyne, the captain of Royal Guard, found Alphys staring at the Garbage Dump's abyss, and became friends with her. Alphys would later develop romantic feelings for Undyne.

When a human child named Frisk fell into the Underground, Alphys watched their journey throughout Underground with the cameras she installed throughout Underground. Later, Frisk encountered her in her labs in Hotlands. Alphys offers to help Frisk on journeys in Hotlands by upgrading their phone and giving hints about the puzzles and traps Mettaton set in Hotlands to kill Frisk. Everytime Mettaton tries to kill Frisk with his traps, Alphys would sabotage the systems to save Frisk.

When Frisk encounters Mettaton in the end of the CORE, Mettaton locked the door he and Frisk was in so Alphys can't intervene their battle. Alphys would later speaks to Frisk through phone that if the switch on Mettaton's back is turned on, he'll become vulnerable. Frisk does what Alphys said, turning Mettaton into Mettaton EX.

After the battle, Mettaton EX have lost his limbs and his batteries ran out. Alphys enters the room, checking out for Mettaton. When Frisk leaves the CORE to go to New Home, Alphys follows them and tells them that to leave the Underground, Frisk must kill Asgore and take his SOUL before leaving and taking Mettaton to her lab for repairs.

Later, Frisk would help Alphys about getting to be more confident to confess her feeling to Undyne by having a "roleplay date". During the "roleplay", Undyne overhears them talking about her and approaches. Alphys confesses that she was trying to impress Undyne by making her hobbies sound more scientific. Undyne comforts Alphys before tossing her into a trash can, and continues to reassure her. Papyrus appears during their conversation and takes Alphys out for a lesson in self-confidence. Their training ends early and he sends her home.

When Frisk travelled to the True Lab, some Amalgamates attacked them and Alphys appears to stop them. Alphys explains to Frisk about the past of Amalgamates and how she had a change of heart and will tell everyone about her failed experiments. Alphys then leaves the lab and returns the Amalgamates to their families.

When Frisk confronts Asgore in his castle, Alphys appears alongside Toriel, Sans, Undyne and Papyrus to save Frisk. When Alphys and Undyne met each other this time, they attempt to kiss each other before Toriel stops them.

Alphys asked Papyrus about how did he gathered everyone into the castle, to which Papyrus saying that "A tiny little flower told him to do it" which led to Flowey suddenly ambushing everyone in the room and captured the monsters.

When Flowey attempts to kill Frisk, Alphys and the other monster friends stopped his murder attempts with their magic. Flowey then absorbs the SOULs of every monster and the 6 human SOULs to turn back into Asriel.

After Frisk's battle with Asriel, the latter released all of the SOULs he absorbed to break the barrier. With this, Frisk and the monsters are finally free from the Underground.

After the monsters went to the surface, Alphys and Undyne started dating each other.