After Nana is literally torn apart by Lucy, Kurama, not knowing Nana has disabled Lucy's vectors, punches Lucy in the face, fully expecting to die and not caring because of how precious Nana is to him.
When Mayu gets a new home, a birthday cake, and her dog back in the space of a few panels.
Nozomi, grateful for Kouta keeping a secret for her, takes a Yuka-blow the tsundere meant for Kouta.
Nana is badly outclassed by Mariko, and becomes a plaything to the cruel little girl—-until Mariko hears Nana call for her 'Papa' Kurama, mocking Nana for this and threatening her 'Papa' (who is really Mariko's Papa) Enraged, Nana literally pulls herself together, slapping Mariko around and disabling her vectors when she won't apologize for her threats.
Despite being overwhelmed by and badly frightened by the vicious pedophilic Unknown Man, Mayu fights off memories of her stepfather's rape and keeps the monster busy just long enough to call...
Bando, who kicks this guy's ass and keeps on kicking it even when hit with a spiked poisoned ball—which he then takes out of his own body and shoves it up Unknown Man's ass!
In a subsequent beach battle with Lucy, Bando shows several good tricks, including the ability to dodge Lucy's vectors. Then when Lucy tries to kill Mayu, Bando takes the blow instead, getting split in half while still taking off Lucy's horns.
During the invasion of Maple House, Kouta is as overwhelmed as anyone else, till he sees Mayu's dog Wanta get batted back by one of the soldiers. This so enrages him, he seizes a gun and takes Nousou, the leader of the force, hostage. When Nousou taunts him that Kouta wouldn't kill him, Kouta agrees—and threatens to blow his jaw off instead...
This ends up getting him shot, which enrages Nyuu—Nyuu, not Lucy—into being able to use her vectors. She tears apart the invasion force, her horns now immense, doing so not for sadistic fun, but to defend her family. Afterward Lucy does wake up again and urges Nana to take care of them as she departs Maple House for the final time. Nyuu shows this badassery again when she tries to rip Kakuzawa a new one after being taken prisoner by him again.
When Barbara, one of the clones of Mariko pursues Nana for the 'crime' of living in peace with Humans, Nana is able to kick her butt all over town—till Kurama is taken hostage. Kurama gets his own again when he emerges from a months-log mental fog to kill Barbara to protect Nana, realizing that while it's his fault Mariko died, in order to truly atone, he cannot make the same mistake with Nana, the only one he has left.
Lucy using her powers to brutally execute her tormentors. While it was a Start of Darkness, watching the little monsters finally get their long overdue comeuppance (and the ringleader's fear just before dying) was infinitely satisfying
Bando says he owes Mayu a kill for saving his life, then changes his tune when he realizes Mayu knows where Nyu is and starts beating her. Mayu pulls out his phone number, asks him to help her stop the big guy who's beating on her, and says he's not much of a man. Even Bando realizes that she's dead on the money and lets her go. Let's repeat: a fourteen-year-old Heartwarming Orphan has more balls than the Rated M for ManlyPsycho for Hire who's out for blood.
In the anime, Kurama letting himself blow up along with his diclonius daughter deserves a mention, along with helping Nana escape in an earlier episode.
Lucy and Bando's fight in episode 2. Bando figures out he just needs to stay at least two meters back, and Lucy's vectors can't reach him. Cue Lucy throwing a boat at him.
Episode 8, when the kids cross the Moral Event Horizon, and Lucy 'awakens' after a passionate scream.
Kouta gets several as well, including getting shot several times to save his friends family. Most importantly taking a bullet for Lucy even after he figured out she killed his dad and sister just because he couldn't stand losing another family member, even Lucy. Also combined with Crowning Moment of Heartwarming the several times he takes one of the girls into his house and makes them part of his family with barely any hesitation, just because they need someone to care.
Near the end of the manga: Kouta has a fatal gunshot wound, Lucy/Kaede's body is already at limits from a abortive attempt at avenging the aforementioned fact on a global scale (which ended in technically minor damage to the neighbouring city), and JSDF air and maritime forces are already scrambling to take her out with their full firepower - fighter jets, warships, missiles, the whole works. What does Lucy/Kaede do? She proceeds to sing the title song Elfen Lied while patching up Kouta's body on a cellular levelandblasting the JSDF forces out of both sky and sea, simultaneously. And she knows full well that she's going to end up with a terminal and ultimately fatal Superpower Meltdown from the effort.
Chapter 63, even better with Tchaikovsky as background music.
Almost anything Lucy does that isn't totally horrific or undeserved could be this for her.
YMMV, but Mayu's amazing courageous act near the end of her backstory. She is sexually abused by her stepfather. Her mother hits her and clearly blames Mayu for his problems. Then one day, Mayu tells the bastard that she is done with this, and gets the fuck out of there. That requires a huge amount of bravery, and Mayu proves she had it.