In BEAST INSIDE, everything involving Ryuusuke going berserk. It's very heartbreaking to see a member of the Peston team, a group of mercenaries, being in despair when the audience just saw them being one big family. It wasn't exactly easy for the rest of the team members either. They all had to convince themselves that the job comes first, and even then there are visible signs of hesitation. There was even a small glimmer of hope that Ryuusuke might pull through. Unfortunately for everybody, it doesn't work out that way.
The end of KILLING DAY. Mamoru is showing signs of awakening.
LOST IN THE FOG follows up on this as Mamoru finally cracks, and Fuku, the first to take notice last week, arrives too late as Mamoru has already taken Misaki's arm right off just to chow down on it. Fuku prepares to Mercy Kill Mamoru on the spot, but of all people Misakiis the one to plead for his life. And when it's really over, Mamoru finally realises what he'd done in an apparent daze, and breaks down further.
The Season FinaleM has Haruka, Mamoru, and the surviving Amazons trying to live in peace away from humans but they have to constantly fend off attacks from Jin and Haruka has to Mercy Kill any of the Amazons that awaken and go wild.
The extermination team begs for Mamoru to come back with them, but he walks away from them as he starts to cry.
In RAMBLING ROSES, Mamoru finally returns. Only this time, he's no longer the kind, crybaby manchild he was. Having become so jaded by the killing of Amazons by humans, he now wants revenge by hunting humans in return. He has now become a leader for the Amazons, gaining a new form and adopting a calm, stoic and rather badass attitude. Seeing the kind and gentle Mamoru becoming so ruthless is just heartbreaking.
SCHOOLDAYS is a gold mine of these:
The Rose Amazon from the previous episode, Shuya returns. It's revealed that the woman helping him wasn't just his girlfriend but his fiance. He apologizes that because of him she was injured which she brushes off as she loves him. He states that he can't imagine a life without her but at the same time he wants to eat her the most. She allows him as he falls to his primal nature, crying as he does.
This episode was just hard for Haruka. First Mamoru tells off Haruka for just protecting but not fighting for them and Haruka realizes that Mamoru has gone too far to be reasoned with. Then he sees that Mizuki is perfectly willing to kill him if needed. The two people he wanted to protect are now willing to kill him.
In this episode both Mizuki and Fuku make the decision that if need be that will turn against their loved ones. Mizuki showing this by shooting at Haruka while Fuku returns his coin necklace to show that he has turned his back on his friends.
In UNDER WRAPS, the implication that the Amazon that was with Chihiro when he was found was Nanaha, who had been eaten and infected by her own son.
Seeing how happy Chihiro used to be growing up with his mother compared to what his life is like now.
The expression on the young Chihiro's face when he realizes just what he had done to his mother.
The implication that Jin is is willing to kill his own son, his own flesh and blood. The fact that he had lost sanity that much to kill his own child, the child that he had with the woman he loved, is heartbreaking.
Even at the fact that he's willing to lose his humanity to save the human race from Amazons.
We get to show who Iyu's father was before he transformed into an Amazon and was by all accounts, a kind man and loving father.
Nanaha, who had stayed by Jin's side at his lowest point and nursed him back to health, chose to abandon the man she loves to protect their son from him.
Seeing the remaining original Amazons losing faith in Haruka because he refuses to kill Jin to stop his slaughter of them.
Jin finding some of Nanaha's clothes and things in the abandoned petting zoo where she hid for a while and breaking down crying as he remembered her.
Chihiro discovering that he is the source of the outbreak and recalling how he attacked and ate Nanaha.
Chihiro desperately trying to get Iyu to say anything to him as he about to put into stasis.
Chihiro's My God, What Have I Done? when he wakes up and sees the carnage from his true from rampaging and killing nearly all the 4C personnel.
WAY TO NOWHERE:
Chihiro's Trauma Conga Line in this episode: his slaughter at 4C starts to sink in, he nearly gives into his instincts to eat another human, gets attacked by Iyu and 4C, and fights against his father who wants to kill him because he claims Chihiro's mother told him to. His last scene of the episode has him collapsed in the tall grass, crying while calling out to his mother, saying that he's hungry.
Kouta's mother, whose medical bills are the sole reason he joined 4C, drank from a contaminated water cooler and left her assisted living facility to find him. Kouta runs into her on the road and she recognizes her son before turning into an Amazon.
What's even worse is that the last time Kouta's mother appeared on screen, she couldn't even remember her son and assumed he was a doctor. The minute Kouta finds her after getting off the phone, she's able to recognize him and call him by his name. It took an accidental infection of Amazon cells for her to remember her own son.
Nanaha is shown to have survived Chihiro's attack on her but has turned into an Amazon herself and is also the secondary point of origin for the Amazon outbreak.
XING THE RUBICON
Chihiro finding some hamburgers and to his despair, he finds them disgusting and can't eat them.
After Chihiro and Nagase get to talk, Chihiro tearfully admits that everything that is happening is his fault from his mother's death, the new Amazons, Nagase's friends' death and to Iyu becoming an Amazon. But despite that he still wants to live. You can tell Chihiro has a lot of disgust towards himself for this simple desire.
When Mamoru wakes up, he sees NPS surrounding him and he starts smiling. Showing that despite what he said, he still cares about the team. As the team tries to reach him, you can see Mamoru struggling between rejoining them and his hatred. Sadly his hatred won out and he runs away.
Every single time Chihiro and Jin fight. Especially as the end of the fights, Chihiro is tired and bloody as his father tries to kill him.
Fuku appears covered in blood and with a deranged look in his eye demanding a HP round. It's easy to see that killing his mother didn't do his sanity any favors.
YELLOW BRICK ROAD
Fuku meeting with the other members of NPS as he reveals what he did to his mother and states that they should have never left Mamoru alone those 5 years ago as he breaks down crying.
Jin meets Nanaha and doesn't recognizes her till she leaves. He then meets Haruka and Mizuki that reveal that Nanaha became an Amazon. Jin tears up at the implication and declares that he'll end this. Haruka begs Jin to leave this to him as Jin refuses and even eats some of Nanaha's tentacles that he ripped off earlier as proof as he walks away.
Iyu fully remembers her father killing her family and herself. She under goes a massive Freak Out and attacks everyone till she exhausts herself as she repeats her father killed her and she was in so much pain. Chihiro then gives her a needed Cooldown Hug.
Mamoru finds himself surrounded by NPS with their weapons ready, showing that they are going to hunt him.
Jin waits at the beach as Nanaha finds him. He even happily waves at her before remember what it means that she's with him.
Chihiro and Iyu hugging each other tightly as Kurosaki's squad unloads bullet after bullet into the two. It takes Nagase directly calling the soldiers out and manhandling Kurosaki to get them to lay off.