Alphyne

Alphyne is the femslash ship between Alphys and Undyne from Undertale.

Canon
If the player befriends Undyne, she tells about Alphys.

The first hint of Alphyne is during Mettaton's Quiz Show when Mettaton asks who Alphys has a crush on and the player answers Undyne. The answer shows up as correct (this also happens if the player chooses Asgore or the human).

Afterwards, if the player is on a True Pacifist Route, Undyne asks Frisk (the human) to deliver a letter to Alphys. Frisk does that, but Alphys assumes the letter is from the human so the two go on a date. Alphys mentions that the contents of the letter werr "passionate". Undyne has written this letter. Undyne interrupts the date and Alphys says that she and Frisk were practicing. Undyne and Alphys end up together after the date.

Before the True Pacifist boss fight, when all of Frisk's friends unite, Undyne and Alphys are both there and run across each other. When Asgore is heartbroken and crying for Toriel, Undyne mentions that 'he will find other fish in the sea'. Alphys cuts in and mentions 'yeah, just stop going after furry boss monsters and just get to know a really cute fish?" This creates a small moment of awkward tension beetween the two. Mettaton cuts in and begs them to kiss because 'the audience is dying for some romantic action.' Undyne immediately tells Mettaton to 'shut up' and comments on 'the nerve of that guy', however, Alphys agrees that they should kiss. Undyne hesitated, then agrees. They are about to kiss, when interrupted by Toriel.

In the credits of the Pacifist Route, Undyne kisses Alphys.