"2.14 Jiken" is a mystery and romance manga that centers around a series of interconnected events tied to a tragic incident on Valentine's Day. The story begins with the death of a high school student named Rika, who falls from the school rooftop on February 14th. Her death is initially ruled a suicide, but her classmate, Shun, becomes suspicious after discovering a cryptic message in her notebook. Shun, along with his childhood friend Yuki, begins to investigate the circumstances surrounding Rika's death, uncovering a web of secrets, lies, and unresolved emotions among their peers.

As the investigation progresses, it becomes clear that Rika's death is linked to a love triangle involving herself, Shun, and Yuki. Rika had feelings for Shun, while Yuki harbored unspoken feelings for Rika. The narrative delves into the complexities of their relationships, exploring themes of unrequited love, guilt, and the consequences of miscommunication. Flashbacks reveal Rika's struggles with her emotions and her attempts to navigate the tension between her feelings for Shun and her friendship with Yuki.

The story also introduces other characters who play significant roles in the unfolding mystery, including classmates and teachers who may have had motives or knowledge related to Rika's death. Clues are gradually uncovered, pointing to the possibility that Rika's death was not a suicide but a result of foul play. The tension escalates as Shun and Yuki confront the truth, leading to a dramatic and emotional climax that ties together the events of that fateful Valentine's Day.

"2.14 Jiken" combines elements of mystery and romance to create a narrative that is both suspenseful and emotionally charged. The characters' relationships and personal struggles are central to the plot, driving the investigation and revealing the deeper layers of the story. The manga effectively balances its exploration of human emotions with the intrigue of solving a mystery, making it a compelling read for fans of both genres.