What type of mixin allows to transform both X and Y?

I am trying to implement a class using the sklearn classes to convert both X and Y. But in the sklearn source code I can only find the X transform (for example, kernelPCA):

https://github.com/scikit-learn/scikit-learn/blob/7389dbac82d362f296dc2746f10e43ffa1615660/sklearn/decomposition/kernel_pca.py

Definition:

class KernelPCA(BaseEstimator, TransformerMixin)

How this class (which transforms both X and Y) should be organized? And from which sklearn classes should it inherit?