Then on a Sunday go to Naganiki Shrine and go to the bench at the lower left corner and talk to that skinny dude and if your academics is high enough you will get to pick from three choices (not sure if the choices matter but i always pick "almost zero").
And after that he will mention his pen.
So go do whatever. Then when you get back to the dorm in the evening talk to koromaru and choose to pick up the pen when given the option.
Not changing this until people start realizing that reality TV syndrome is a poison!