I didn't put this in the notes, since I'm still in the process of fitting the pieces together, but just as a bit of commentary, there's definitely some sort of pattern going on with the human characters' names.
首藤レン
綿谷メイ
茅木メル
菅野ルカ
All of them so far are 4 characters, their family names being kanji (including a plant) and their given name being katakana.
At least in the case of the girls, I'm pretty sure they're named after the Gospels.
Mei Wataya -> Matai (Matthew)
Meru Kayaki -> Maruko (Mark)
Ruka -> Ruka (Lucas)
(that one was the tipoff)
I don't know what Ren's name could be in reference to, though. Yohane (John) is what's left, and he doesn't fit.
Also can't tell if the kanji in their names have any particular relevance. Again, they all have plants (wisteria, cotton, miscanthus, sedge) so there's probably a theme, but whether it ties into anything biblical I can't tell.
Also, and this one feels pretty self evident, I think B stands for Best Girl.