>>535706392
Real Ruka is dead. This happens before her debut.
Narby Ruka/Pom-pom picked up the slack. So Pom-Pom became Ruka.
Narby Ruka had to play catch up hard to eventually become "her".
Gigaspoiler: She never got her corpse. She only took her form. So she literally had to start from nothing.
Narby-Ruka, who, despite being a narby, still resonated with Ruka's love for her mother after years of observing them together.
Ruka's mother eventually died to a supposed similar accident. Because of said attachment to Ruka's mom, Narby-Ruka lost all her motivation and left the band.
But as this sis says >>535706983
Just keep reading. You don't have to hover over the spoilers.