Episode 27 is one of Amu's worst days. It starts off positive after Dia's egg appears and she finds out she's in the same class as Tadase, but with Nadeshiko gone to Europe, she feels nervous about the new class and wishes she had some female friends there. Then Rima shows up. When the rest of the class dicusses her before she's introduced, some speculate about her being the new Queen's Chair, which doesn't help the mental hole left by Nadeshiko's absence. Then when she is introduced and sits next to Amu, Amu sympathises with her as a fellow New Transfer Student and tries introducing herself while forcing a smile, but she's shot down by Rima's cold demeanour. After school, she spots Yaya spying on an X Egg but blows her cover calling out to her. Yaya, irritated at this, tells her to "stay out of the way". Eventually Yaya has trouble and Amu decides to help her out anyway, but has enough trouble with that as well. When all the above starts to get to her, she's reminded of Nadeshiko again, and feeling left behind, she runs all the way to a classroom, hiding her tears. In said classroom, some boys from her class are inconsiderately holding a "cutest girl ranking", putting Rima at the top and Amu second, calling her "normal", disappointed in how she's started dropping her cool façade, saying she "hasn't seemed like herself lately". After this, she starts getting really depressed, reflecting on everything that happened, and questions what exactly being herself means. And to top it all off, the result is Dia's egg getting marked with an X. It's a perfect representation of how multiple small negative events piling up over an entire day can result in one feeling very emotionally drained.
Betty's death can definitely be this for people who've ever lost a pet.
Though not quite as sad as some of the other stuff listed, when Tadase confesses to Amu, and is later at her house, Ikuto walks out of her room and confesses that he'd been there the whole time, including during Tadase's confession. Tadase's reaction was heartbreaking for everyone involved, including the audience. And then the aftermath; after Tadase left, Amu tells Ikuto that she HATES him, and leaves the room to go after Tadase. Ikuto walking away from her house saying that nobody should get closer to 'a black cat of fortune' (basically calling himself a black cat of misfortune) does not help either. And that was the last time we see Ikuto before Easter createsDeath Rebel.
Utau transforming with X-Dia has a sad undertone to it. We learn that her two guardian characters -Iru and Eru-, are basically two sides of a same coin that Utau feels when she sings two different kinds of songs (despite Iru's rather devilish appearance, she's not actually meant to be used for evil). When Utau begins fulfilling that dream of making people listen to her singing for something other than her passion for singing and making people feel a certain way by producing songs such as "Black Diamond", she's defying the very thing that made Iru and Eru exist. She, herself is shown to feel distaste and dissatisfaction at her own actions that she has to upkeep to 'make Ikuto happy'. The big irony is that no matter how much she rags on about Amu's weakness, transforming with Dia actually shows Utau's weakness in betraying herself. A guardian's character whole purpose and power stems from the owner's heart and their wishes to become a certain way or do a certain thing, the power she's using for her songs isn't even hers... It's Amu's. And to add to that, Dia was born from Amu's secret admiration for Utau, too, as shown by her normal design. She's basically bonding with a broken, disheartened version of herself and Amu who believes perfection only exists in the hearts of people who fight without heart or ever making mistakes.
Ikuto and Utau's back-story is pretty heartbreaking, especially regarding Ikuto. Their father abandons them to avoid being forced to give up the violin and run Easter, and their mother is so devastated that she falls ill and is unable to care for them. They have to move in with the Hotori family, and Tadase's mother treats Ikuto very poorly due to being jealous of his mother (this was toned waaay down in the anime). Ikuto then has to go on the run and avoid being forced into working off his father's debt to Easter, and that means leaving behind his little sister and best friend. He's forced to turn the other cheek when Tadase confronts him about it so he doesn't get involved in all of Ikuto's problems and potentially get hurt. He goes looking for his father and cannot find him, and when he returns, he is forced into Easter anyway with the threat that if he doesn't do their bidding, they will go after his mother and Utau. He spends many years alone and searching for the Embryo to free himself until one day he decides to take the Dumpty Key back. This involves going to Tadase's house, where he finds that Tadase's beloved dog Betty is dying, so he plays her a melody on the violin to help her go peacefully. Tadase comes and sees this, misinterprets the scene and becomes angry, and Ikuto cannot explain, because Tadase might get dragged into Easter with him. He then runs off with the Dumpty Key leaving Tadase to believe he's a thief and a curse that killed his dog and made his grandmother fall ill. Ikuto has spent half his life isolating the people he loves because he doesn't want them to get hurt. And that’s just leaving out all the crap he is put through during the Death Rebel arc. All in all, the Tsukiyomi siblings need a big hug and a blanket.
Kairi's confession to the Guardians. Sure, we knew all along, but the creepy smile on his face, and the visible shock and hurt on everyone's faces as he mocks the friendship they thought they had just feels like a stab in the chest. Especially when we saw his inner conflict and some of the genuinely sweet moments he had with Amu and the others. Even though they make up later.
