Happens on Episode 8 and there are 27 episodes -- although like one and a half of them are just filler ("compilations"). So make that 26 episodes, 8 x 3 is 8, 16, 24. That's almost a third, right? You said it "wasn't even a fourth". Eight times four is 32, if you can't do math. Also, it's the biggest plot twist if you actually liked Kamina -- which I did.
/gives a fuck about nia being an anti-spiral robot
/gives a fuck about her disappearing at the end