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in addition; furthermore
above (which); on top of (which)
「その上」 has another reading with different meanings.
彼は頭がいい。その上、優しい性格だ。
He's smart. In addition, he has a kind personality.
雨が降っている。その上、風も強い。
It's raining. Furthermore, the wind is strong.
その上、値段も安い。
On top of that, the price is low.