The $S_8/{\sigma }_8$ tension in the large-scale structure can be explained by decaying dark matter with an almost degenerate spectrum and small enough decay width. Here we propose the Gemini dark matter model, which contains a heavy mother particle ${\chi }_3$ and two twins ${\chi }_{1/2}$, which are almost degenerate in mass and are produced at the same time. The dark sector is charged under the same Froggatt-Nielsen symmetry that can explain the hierarchy of the Standard Model Yukawa couplings. The slightly heavier ${\chi }_2$ decays into ${\chi }_1$ and the axionic component of the flavon, which washes out the small-scale structure and resolves $S_8/{\sigma }_8$ tension. We present the production mechanism of Gemini dark matter and viable parameter regions. We find that, despite the preferred dark matter mass being $O\left(1\right)–O\left(100\right)\mathrm{keV}$, they constitute cold dark matter. The Gemini dark matter model predicts an abundance of dark radiation that will be probed in future measurements of the cosmic microwave background.