I thought the title refers to Mikoto and Takase progress, but alas, it was not. Should have known progress with the main couple is as rare as a normal person in this world.
I think is when she graduated, confessed her feelings and was told no because she was still a minor, then tried to jump froma tree, hence the "10 years old birthday confession and forced fait accompli" plan.
She's climbing the stairs tree to adulthood
Nah just kidding, she immediately jumped him as soon as she turned 18 that a previous page implied. I've been trying to find which page was that...
EDIT: found it
Because of the title my read was that she got that energy from happiness and you just want to use up that energy for something in those situations, like trying to climb the nearest tree. But knowing the author I am likely 95% wrong ...