亜 is one of the most commonly used Japanese kanji, and it also has a lot of special readings in addition to the standard onyomi and kunyomi readings.
ONYOMI 音読み
つ.ぐ tsu.gu
KUNYOMI 訓読み
ア a
Examples
あ!まずい!ガソリンが切れてきた。Oh, no! We’re running out of gas.あ!蝶々がいる!Oh, there’s a butterfly!あ、汽車が来た。Here comes the train.あ、流れ星だ!Look! There goes a shooting star.あ、停電だ。Oh, the lights went out.あ、切れちゃった。Oh, I was disconnected.あ、そうだ。まゆに変なことしたら、背骨を折る。One more thing. If you try anything on Mayu I’ll break your spine.ん?あ、悪い。Huh? Oh, I’m sorry.あ、上書きしちゃった。Uh oh, I saved over it.あ、今度ケー番交換しませんか?Ah, could we swap our mobile numbers next time?