Well, in 'the flash dark barry fanfiction', a frequent theme is the loss of control. As Barry turns dark, he often loses the control he once had over his powers and his actions. Also, the theme of isolation is common. His friends and family may start to distance themselves from him, which makes him even more isolated and prone to further darkening. There's also the theme of redemption, as some stories explore whether he can come back from his dark state.
In these fanfictions, the theme of power corruption is quite common. Barry's great speed powers can be corrupted in various ways, leading to his dark side emerging. Another theme is the exploration of his psyche. We get to see what really makes Barry tick when he's pushed to the edge. And the theme of identity is also there. As he becomes dark, he may question who he really is, is he still the hero known as The Flash or something else entirely.
Another theme is emotional pain. His relationships with friends, family, and love interests can be a source of hurt. For example, a broken friendship or a lost love.
Another theme is the importance of support. His friends like Cisco and Caitlin play crucial roles in helping him recover. They provide medical help, emotional support, and sometimes even give him the motivation to keep going in the face of pain.
Power exploration is also a theme. Since the OC is often a new addition with unique powers, the fanfiction may explore how these powers work, how they can be controlled, and how they interact with Barry's speed - related abilities. This can lead to some really cool and creative plotlines.
One common theme could be the power struggle between them. Given their complex characters, fanfictions might explore how they vie for control or influence in different situations.
Another theme is friendship or begrudging respect. Since they are from different 'sides' initially (Barry as a hero and Leonard as a villain or anti - hero), stories often explore how they come to see value in each other. For example, they might start off as enemies but end up as allies, and the journey of how that happens is a common theme. It can involve things like Leonard using his skills to help Barry in a tricky situation and Barry showing Leonard there is more to heroism than he thought.
One common theme is his relationships, like his love for Iris. Many fanfictions explore how their relationship evolves or faces challenges.
Love is a very common theme. Their relationship is at the core of many fanfictions. Another common theme is adventure. Since Barry is The Flash, fanfictions often include them going on adventures together. For example, fighting new villains or exploring new dimensions.
One great 'the flash dark barry fanfiction' story is 'The Darkening of Barry Allen'. It explores a version of Barry where his powers take a dark turn. Another could be 'Dark Barry's Ascent' which shows his journey into a more menacing character. There's also 'Barry in the Shadows' that delves into his darker side.
One common theme is the development of their relationship. It could be a romantic relationship, exploring how they fall in love and deal with the challenges that come with it.
One common theme is friendship. Since they are two different characters, their journey from strangers to friends is often explored. Another theme is growth. As they interact, they both grow as individuals. For example, they might learn new skills from each other.