Yakuza no Obentou - Tokidoki Yankee o Soete

The main character of this work is Fubuki Kaburagi, a 22-year-old beautiful woman who is passive in love, moderate in her studies, and has lived her life carefree.

Fubuki, who inherited her lunch box shop left by her unpredictable mother, spends every day rambling with her doting younger brother Siu while paying off the debts of her shop. One day, a yakuza who heard about her good looks in Fubuki visits her shop and offers a bet. The bet is, ``If you can prepare the unpaid amount of the previous month and the debt of this month with only the sales of the bento shop within 3 days, the remaining debt will be completely gone.”

Fubuki tries her best to sell boxed lunches with the help of her childhood friend Riku, a yankee, but it doesn't all go well...

source: https://www.mangaupdates.com/series/u06x3u4/yakuza-no-obentou-tokidoki-yankee-o-soete