Siblings tend to have one similar syllable in their names

Siblings tend to have one similar syllable in their names in Japan. I have a feeling that the Tajima siblings are named similarly.

Theory: So if Yukine’s sister is named Yuka, then it is highly possible that Yukine’s real name is Haruka. Quite a girly name, but I just have a gut feeling. ╮(￣▽￣)╭