Mecha gains enormous power, turns red.
Half of an areola visible only for an instant, "concealed" by frenetic bouncing
The climax of "Full Swing" seems to be a direct descendant of Neon Genesis Evangelion's Sahaquiel fight. The "transformation" element of the hurtling object changing form as pieces break off was in FLCL first, then was reappropriated for 2.0.
EDIT: Ah, right! The ending!
SPOILER: Show
Wings
Environment turns red, stuff starts to float as people look up in shock
Red halo, glowy heart