In "Don't Toy With Me, Miss Nagatoro" Volume 4, the rollercoaster relationship between Nagatoro and Senpai reaches new heights of playful yet complicated interactions. 

Armed with a lollipop, a bathing suit, and an ear-piercing gun, Nagatoro introduces new elements into their interactions. The lollipop may become a prop for her teasing, adding a sweet twist to the banter. The mention of a bathing suit suggests the inclusion of scenarios that involve more personal and potentially intimate situations, possibly taking their relationship to a new level of closeness.

The ear-piercing gun introduces an element of surprise and excitement, showcasing Nagatoro's inventive methods for keeping Senpai on his toes. Each of these elements contributes to the progression of their relationship, teasing out different aspects of their personalities and emotions. The phrase "closer to something more than 'just friends'" hints at a potential development in their relationship.