One common theme is isolation. Castiel often feels alone in his pain, whether it's due to his otherworldly nature or the actions of those around him. Another theme is betrayal. He is frequently betrayed in these stories, which causes him deep emotional harm. For example, when his allies turn on him or when he is misled by false friends.
One good 'emotionally hurt Castiel fanfiction' is 'Fallen Angel's Pain' which delves deep into his inner turmoil and emotional wounds. It shows how he copes with the rejections and losses he has faced in his journey. Another one could be 'Castiel's Silent Sorrow' where his emotional distress is palpable as he struggles with his loyalty and the changing dynamics around him.
I remember reading a fanfic called 'Castiel's Wounds'. In this story, Castiel is severely injured during a battle with demons. The fic focuses on how Sam and Dean try to help him recover, and the relationship dynamics between the three are really well - written. It shows Castiel's vulnerability in a very believable way. There's also 'A World of Hurt' which explores Castiel's hurt in a post - apocalyptic setting, adding an extra layer of tension and drama.
One common theme is redemption. When Castiel is hurt, often the story will revolve around him finding a way to redeem himself, whether it's from a mistake he made that led to his pain or just from a sense of lost purpose. For example, in some fanfictions, he might have been hurt because he trusted the wrong entity and then has to make amends.
In a lot of these fanfictions, the theme of unrequited love can play a part. Ruby might develop feelings for someone who doesn't return them, and this causes her emotional distress. Additionally, the theme of being misunderstood is common. People around Ruby may not understand why she's acting a certain way because of her hurt, which just adds to her pain and isolation.
The theme of Castiel being tortured, either physically or mentally, is quite prevalent. It could be at the hands of demons or other angels. And then there's the aftermath of his hurt, like his struggle to regain his strength or his faith. Also, his relationship with Dean often takes center stage during his time of hurt, with themes of Dean's protectiveness and Castiel's dependence on him.
There's also 'Castiel's Painful Journey'. In this fanfiction, Castiel endures a great deal of hurt due to a powerful spell that backfires on him. It details his journey of recovery and the relationships that help him through it. He has to face his own insecurities and fears as he heals, which makes for a very engaging read.
I'm not sure about a specific title right now, but you can try searching on fanfiction platforms like Archive of Our Own. Look for stories tagged with Ruby and 'emotional hurt'. There are likely many great ones there. Usually, in such fanfics, Ruby might face betrayal or loss, which makes for a very emotional read.
In many such fanfictions, Castiel's character development often revolves around his newfound vulnerability. With his hurt wings, he can't be as strong or as mobile as before. This forces him to rely on others more, which makes him more empathetic and less of the aloof angel he used to be.
One common theme is loyalty. Gabriel's protectiveness shows his loyalty to Castiel. Another theme is sacrifice. Gabriel might be willing to sacrifice his own well - being or position to keep Castiel safe. For example, he could risk getting on the wrong side of other powerful angels.