>>49418270
Apparently the explanation is May = Mei and then 15 as in the 15th element in the periodic table (P) which is read as "rin" in japanese, so it ends of being meirin which is meiling.
Here is the direct explanation from the pixiv tag
>東方Project「紅美鈴」のキャラの日の一つ。「５月(Mayめい)」「原子番号１５が"リン"」の語呂合わせ。