Why these characters matter
The anchors worth learning first are the ones with the fewest lookalikes. Darling in the FranXX has 5 characters, all listed for 2018, where pink hair appears on only 1 of them, while white covers 2 — so a distinctive hair colour is often enough to locate the right cluster.
Learn Zero Two first, then the candidate it is most often confused with: Hiro and Mitsuru agree on 4 of the five clue traits. That one comparison removes the most common failure in Darling in the FranXX mode.