Ritsu Onodera, a proud literary editor, faces envy at his father's publishing house. Determined to prove himself, he switches to Marukawa Publishing, only to end up as a rookie manga editor in the hectic Emerald department. Here, he encounters his former high school love, now the demanding editor-in-chief Masamune Takano. Their past heartbreak haunts Ritsu, hindering his willingness to love again. As they reunite, Takano is resolute on hearing Ritsu confess his love once more. 'Sekaiichi Hatsukoi' delves into the intertwined romances of three couples in the manga world, each experiencing the bloom of their first love.