One of my favorite JDramas of all time. The characters in this show are all so amazing. Especially the main character. I also really like the main support girl. And of course this JDrama has an amazing ending song but I digress.
The JDrama is about who gets to become the successor of a major Yakuza clan in Japan. You so you Makio and Mikio of the Sakaki family vying for the leader position. One is the ultimate fighter with no brains, and the other is the weakling with uber intelligence.
The older brother with no brains is the show's main character. His father asks him to go back to High School and graduate, and by graduating he'll earn the successor position.
So this 30 year old Yakuza badass infiltrates a high school and starts studying. This Jdrama is all about the life Makio and how he adapts to the high school environment. It's funniness is based on the fish out of water principle since you know a yakuza leader isn't the type to be in high school.
He has a hard time adapting to the teacher's authority. And also he gets bullied at school because he can't just beat up the weak bully etc. etc. What I really liked about this show was the high school life.
I really wish I went to high school in Japan. I think that would've been so much fun. There's an ongoing joke about Agnes pudding. I don't get how pudding can actually be that good but oh well.
tl;dr - watch this JDrama. It's crazy stupid funny and entertaining.