Mako-Chan Kaihatsu Nikki.

For the first time in her young life, high school student Makoto Himemiya receives a love confession from a boy! Before he even gets an answer, however, he tries to run away – a safety measure. Fortunately, Makoto is able to stop him in time and give him an answer to the confession: yes, she wants to be with him! Overjoyed, she goes home, but because her heart is pounding so much with joy, she has to find something else to do to calm down again. Promptly, her panties drop and she catches herself masturbating with the thought of her first boyfriend. However, her brother Takeshi moved back home some time ago. And just at this most inopportune of moments, he bursts into her room…