Books in the Don't Toy with Me, Miss Nagato series

It's actually happening! Senpai and Nagatoro get closer than ever before when they visit an aquarium together. But the fledgling couple isn't alone. They're being watched by two opposing parties--Nagatoro's meddlesome friends who worry Nagatoro might ruin Senpai's innocence, and the Sunomiya duo, who will fight to let love take its course. Depending on which side gets its way, this long-awaited rendezvous could become a date with destiny or a date with devilry!

"A new rival enters the scene in the form of Shikki, one of the girls on Nagatoro's Judo team. Shikki proves to be a formidable opponent on the mat, but she also becomes a handful of trouble (and other things) for Nagatoro and Senpai when she discovers them both in the wrong place at the wrong time. Now, Senpai stands to be on the receiving end of a visual assault like no other, but does Nagatoro have what it takes to save him (and his virtue)?"--