Servamp
So obviously Sakuya became a vampire through Tsubaki due to him being on the verge of death. I imagine the trauma and PTSD that comes with being forced to jump from a large height to your impending death would be a key factor in a lot of things. For example, a fear of heights- Sakuya wouldn’t be able to go anywhere with tall heights due to memories and experiences.
But also, being a vampire can mess with social relationships and communication. Sure, Sakuya managed to keep his vampire side relatively well hidden for a long time in his friendship with Mahiru, but eventually he couldn’t keep it hidden anymore. Craving blood would be a big setback in the making-friends department, and it would be hard to resist it forever unless he had a full access to blood without causing too much harm.
Not only that, but Sakuya is generally a loyal or deeply attached character, in the fact that he gets attached to people easily. Although he does not exactly like all of Tsubaki’s actions, he tolerates them out of a sense of loyalty, because Tsubaki was the one that saved him when he was dying. He also is deeply attached to Mahiru as a friend and shows a deep sense of loyalty and compassion for him, too. It’s probably why he often gets so deeply rooted in conflict between the Servamps and their Eves.
With all these factors in mind, adding to the fact that Sakuya probably ages slow compared to other humans, he's probably a very lonely character. He was made Tsubaki's subclass at a young age (as a teenager) so it's probably more awkward for him, what with all the hormones that probably run through his body constantly.
This is all I have for Sakuya.
I just think seeing more fics centered on Sakuya would be cool ya know?
But I don't think I'd be able to write it