A woman who chose death wakes up with a stranger's heart and has to live someone else's life instead. The show doesn't waste time pretending this is just a plot device, it's the entire point, and it breaks you slowly across fifty episodes by making you understand that taking someone's heart means taking their unfinished business too. The pacing collapses in the back half and drags you through filler that doesn't matter, but the first arc and the stretch around episode 32 remind you why this hurt so much in the first place: a hired killer learning to want to stay alive, one conversation at a time.
A woman known only by her codename Glass Heart survives the unsurvivable: a suicide jump that should have killed her. Saved by an emergency heart transplant, she wakes in a hospital bed with a borrowed heart beating in her chest. But the organ comes with baggage. Fragmented dreams plague her nights, haunting visions that pull her toward Japan and an obsessive need to find the person whose heart now keeps her alive. What she discovers shatters her world: the donor was Kaori Makimura, a woman connected to Ryo Saeba, a legendary assassin and the last person she expected to encounter. As Glass Heart ventures deeper into Ryo's orbit, she finds herself caught between the violent life she's always known and something unexpected stirring in her borrowed heart. Romance blooms where danger should reign, and past sins collide with second chances. Nothing in her training prepared her for this impossible choice between two worlds that refuse to coexist peacefully.