  A novel framework is proposed to extract near-threshold resonant states from
finite-volume energy levels of lattice QCD and is applied to elucidate
structures of the positive parity $D_s$. The quark model, the
quark-pair-creation mechanism and $D^{(*)}K$ interaction are incorporated into
the Hamiltonian effective field theory. The bare $1^+$ $c\bar s$ states are
almost purely given by the states with heavy-quark spin bases. The physical
$D^*_{s0}(2317)$ and $D^*_{s1}(2460)$ are the mixtures of bare $c\bar s$ core
and $D^{(*)}K$ component, while the $D^*_{s1}(2536)$ and $D^*_{s2}(2573)$ are
almost dominated by bare $c\bar{s}$. Furthermore, our model reproduces the
clear level crossing of the $D^*_{s1}(2536)$ with the scattering state at a
finite volume.
