A variation of the BETABETA kanji, the SIDEKICK is a kanji that is 99% of the time, ONLY USED WITH ONE SPECIFIC OTHER KANJI - in ONE SPECIFIC COMPOUND WORD.
The good news is, it turns out you don’t really need to learn sidekick kanji. Once you’ve learned the OTHER, more USEFUL kanji of the compound word, make a flashcard of the whole word, and learn the sidekick that way. More good news: You don’t have to learn the KUNyomi of sidekicks, because they’re seldom used.
KANJIDAMAGE