  There are many theories where a dark matter particle is part of a multiplet
with an electrically charged state. If WIMP dark matter ($\chi^{0}$) is
accompanied by a charged excited state ($\chi^{-}$) separated by a small mass
difference, it can form a stable bound state with a nucleus. In supersymmetric
models, the $\chi^{0}$ and the $\chi^{-}$ could be the neutralino and a charged
slepton, such as the neutralino-stau degenerate model. The formation binding
process is expected to result in an energy deposition of {\it O}(1--10 MeV),
making it suitable for detection in large liquid scintillator detectors. We
describe new constraints on the bound state formation with a xenon nucleus
using the KamLAND-Zen 400 Phase-II dataset. In order to enlarge the searchable
parameter space, all xenon isotopes in the detector were used. For a benchmark
parameter set of $m_{\chi^{0}} = 100$ GeV and $\Delta m = 10$ MeV, this study
sets the most stringent upper limits on the recombination cross section
$\langle\sigma v\rangle$ and the decay-width of $\chi^{-}$ of $2.0 \times
10^{-31}$ ${\rm cm^3/s}$ and $1.1 \times 10^{-18}$ GeV, respectively (90\%
confidence level).
