Kyou no Ashura Meshi

One day, Omori Sizuka, a high school girl who loves to eat and is bullied by bullies, discovers the secret that Akira Kurose, aka "Ashura-kun," the only tough yankee at school, enjoys cooking. The next day at lunchtime, Akira summons Sizuka to the rooftop and asks her to eat his homemade lunch box to keep her mouth shut.

"A delinquent guy likes a chubby girl for who she is but he’s worried about her health cause she’s eating nothing but unhealthy food. So he starts making lunches for her so her diet gets better and then romance begins"

Original Manga:
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