そういやwhich reminds me ..., come to think of it ..., now that you mention it ..., on that subject ..., so, if you say ...

そういや、彼(かれ)は今(いま)何(なに)をしているのだろう？

Come to think of it, I wonder what he's doing now? {which reminds me ..., come to think of it ..., now that you mention it ..., on that subject ..., so, if you say ...}

店主(てんしゅ)：「あれ、そういやあの常連(じょうれん)を最近(さいきん)見(み)ていないな。」

Shop owner: "Come to think of it, I haven't seen that regular customer recently." {which reminds me ..., come to think of it ..., now that you mention it ..., on that subject ..., so, if you say ...}

夫(おっと)：「あ！そういや、昇給(しょうきゅう)したことを言(い)うのを忘(わす)れていたよ！」

Husband: "Oh! Come to think of it, I forgot to tell you that I got a raise!" {which reminds me ..., come to think of it ..., now that you mention it ..., on that subject ..., so, if you say ...}

そういや彼(かれ)は昨日(きのう)の打(う)ち上(あ)げに来(こ)なかったが、どうしてだろうか…。

Come to think of it, he didn't show up at the launch party yesterday, I wonder why... {which reminds me ..., come to think of it ..., now that you mention it ..., on that subject ..., so, if you say ...}

夫(おっと)：「そういや、気持(きも)ちを込(こ)めて手紙(てがみ)を書(か)いたんだ。」妻(つま)：「え？嬉(うれ)しい！」

Husband: "Come to think of it, I put a lot of emotion into writing that letter." Wife: "Huh? That's wonderful!" {which reminds me ..., come to think of it ..., now that you mention it ..., on that subject ..., so, if you say ...}