Repeat A Year! Todome-Senpai

Sato is a high school boy struggling with his grades, but that's the least of his worries. His childhood friend and former upperclassman Waseda Todome wants to spend time with him (the keyword being "former", as she's repeating the first year and now shares classrooms with Sato).
The problem lies with the fact that, while being cute and flirty, she's dumb as bricks, and intends to make him sabotage his own grades because she doesn't want to be alone at the bottom of the school's grade ranks. However, it turns out that she's dumb as bricks when it comes to that too...
Todome's poor planning has some unintended consequences, as it readily reveals that her intentions with Sato do not lie purely within the academic side of things... Will Sato take the hint, notwithstanding Todome's bad clues?

Note: Includes 4 extra chapters.