Until this point in the story, the only perceived competition Nanaki has had have been female, and so she has been able to rationalize her feelings of jealousy as her wanting to be Kanade's best friend, but now that she sees Kanade being close with a guy and still feeling that same jealousy, it'll start to force her to confront the fact that her feelings are deeper than just best friend feelingswth it seriously became a pain in one chapter so easily... amazing power to have author but soooo not needed... ehhhhhhhh
like come on we already had jealousy before but now with a guy character and even worse, she has a weird fixation on her friends perfect gyaru persona outta nowhere ehhhhh