After
bombarding poor Kirihara's journal, and in the context of that, considering Eiji's insecurities at Oishi's BL drama role and all the regrettable time they've spent apart lately- Oishi did as he promised and came up with a list of qualities he liked about Eiji. To distract momentarily from how cute Oishi's costars likely are. And hopefully stave off Eiji's worries.
Since the non-stop sleeping over has not taken a break, he had to sneak the list under Eiji's door as he was out at a Kiva taping after school today and quickly returned to his apartment.
Anyone on or around the fifth floor at that time can feel free to laugh at how stupid and/or suspicious he must have looked sneaking around and slipping notes under doors. He's not good at stealth.