Chestnut tiger butterfly of that day

This is a cover illustration for the book “Nostalgic Boy”.
https://www.amazon.co.jp/gp/product/475625196X?language=en_US&pf_rd_p=7b903293-68b0-4a33-9b7c-65c76866a371&pf_rd_r=H6ZXDBE138ZBJPG4Z6Q9