Tattoos for a Japanese person are taboo in the extreme. At least if they have strong ties to Japan. Tattoos on the neck, I have no idea how bad that is in Japanese culture. In the west a neck tattoo is not generally look at with fondness, often baring a person from some types of job environments, generally office work environments, like the one Aya works at. I wonder if Harry will remain the densest matter on earth, when faced with a massively overt signal that Aya has changed, and not for the better. It's not normal for a (outwardly) cute and bubbly office flower to get a neck tattoo, more so if they are Japanese.
Tattoos with heavy metals will often pool on the brain and are wildly unhealthy, though I doubt Aya got one that has such ink. Anyhow, I think the dev is doing a good job of ruining Aya, thoroughly. Which is the point of the story, though I really like his routes that have Aya get with Harry, with varying degrees of brokenness, ranging from little to nearly catastrophic, tends to pull on my emotions.