[DeepL Translation - needs review] Introduction to Volume 1: Eighteen-year-old Rose, who lives in a boarding school in a deep forest, is selected as one of the candidates for the position of godchild, which entitles her to various privileges. The ritual to decide who becomes a godchild is to submit oneself to a man, and that man is Tokiwa, the commander of the school's administrative unit, whom Roses has always harbored hostility toward. Tokiwa suddenly reveals a surprising fact to Rosa, who...
ブライト・プリズン starts off with our hero, the 18-year-old 薔 (しょう), is trying to escape from the academy he's been raised in since age 3, and failing yet again. What follows is an introduction to the cult he was raised in, who take in male children among their followers in an attempt to find 神子, who are capable of receiving prophecies from the dragon god they worship. 薔 is chosen as one of the 神子 candidates, and the story follows along the trials and tribulations he faces following that, along with main love interest 常盤 (ときわ).
While I overall liked the book and 薔 in general, his single-mindedness in relation to certain things and people made for a bit of a slow middle section personally, when it really felt like the author needed to kill time until the next scheduled plot event, and all 薔 could do was spin his wheels; 薔 has, for better or worse, plenty of time to consider his feelings, so at least by the time the action starts again he's pretty straightforward with it.
Content warnings for the romance in this book: age gap (12 years, I believe) and (this is a legit spoiler for book one) incest, specifically between brothers. Also of note for the plotline in general/R-18 content (and this is also a spoiler for this book): the aforementioned cult is in reality a sex cult: the 神子 have to engage in male/male sex to receive a prophecy, so expect a decent amount of sex.
The grammar was not difficult or unusual; it was maybe around N2. The vocab was a bit more difficult; there are lots of setting-specific words used, and they are only sometimes given furigana at the start of a chapter, so if you can't remember how the word was supposed to be pronounced, you've have to flip back a ways to find it. The specific vocab is pretty heavily used, at least, so sooner or later it should sink in.