This anime starts with a look back at how the main character became a billionaire.
This anime begins by reflecting on the process by which the main character became a billionaire.
この場合、次のような言い方ができますよ。
ーThis anime starts with a look back at how the main character became a billionaire.
「このアニメは主人公がどのように億万長者になったかの回想で始まる」
a look back で「回想・回顧」
ーThis anime begins by reflecting on the process by which the main character became a billionaire.
「このアニメは主人公が億万長者になる過程を回想することで始まる」
to reflect on the process で「過程を回想する」とも言えます。
ご参考まで!