Her darling just loved cats.
The first day they went out together after her love had moved in, she had begged to get one. They walked to the pet store, hands linked, and picked up a kitten. A little calico with a pink nose. Iroha just adored that little thing, naming it Milkpuff for whatever reason. Of course, if Iroha loved it, then naturally Rin should too.
The years went by and the kitten grew into a cat, and then older still. It turned out to be such a healthy and beautiful adult. Iroha loved Milkpuff, too. She would play with it, read with it lying on her lap. While Rin would go out for her jogs, her love was inside with the cat.
She wasn't sure how to feel, at first. It was quite silly of her to be jealous of a cat, of all things. It was an animal. A pet. Surely it didn't matter if her love spent some time with it? Even so, Rin found herself hating it more as time passed. When Iroha called them in for dinner on the nights she made it, she would always call in Milkpuff first. Never mind that she filled up its bowl before setting the table. And she would always act cold when Rin sat by her while she was reading, but when Milkpuff leapt onto her lap, she greeted it with warmth and affection, stroking its white, brown, and orange dappled coat.
Enough was enough.
Her father had given her a gun for her birthday once. For protection, he had said. She kept it under lock in her dresser. Reasoning that she was sort of protecting herself from the stupid feline, Rin grabbed it and stepped into the living room. Iroha sat there with her book, Milkpuff purring on her lap. "Get over here, you stupid cat," she snarled, lifting her weapon. Iroha seemed to freeze in her spot.
And then she stood in front of Milkpuff.
"Hurt him," she breathed, "and you hurt me too." She was so beautiful, so lovely in that moment. Hair swinging loosely from the bun she had pinned it in, eyes bright and wide. She looked almost like she did when Rin first confessed to her, all those years ago. She didn't want to kill Iroha. She wanted the girl to love her, to care for her like always. But she did want that cat with its horrible smirk gone.
bang
And her darling fell down dead.