What does the kanji 亜 mean?

亜 means Asia, rank next, come after, -ous.

亜

亜 (Asia, rank next, come after, -ous)

亜細亜アジア

(1) Asia (esp. "the Far East") (2) Asian; Asiatic

亜米利加アメリカ

America

亜あ

(1) sub- (2) -ous (indicating a low oxidation state); -ite

ジャスティン班長はんちょう、亜あ空間くうかんレーダーに反応はんのう出でました！

Squad Leader Justin, a blip's appeared on the hyperspace radar!

笑わらいで誤魔化ごまかすと、亜美あみさんはさも不機嫌ふきげんそうに眉まゆを寄よせた。

Ami frowned in a very un-amused way as I brushed her off with a laugh.

「亜あ佐美さみ先輩せんぱいが、ヒロシくんが真田さなだ先輩せんぱいとキスした～って泣なき喚わめいていたので」「な、泣なき喚わめいてないよ～」

"Asami was bawling that you had kissed Sanada so" "I didn't bawl!"