  We study (i) asymptotic behaviour of wild harmonic bundles, (ii) the relation
between semisimple meromorphic flat connections and wild harmonic bundles,
(iii) the relation between wild harmonic bundles and polarized wild pure
twistor $D$-modules. As an application, we show the hard Lefschetz theorem for
algebraic semisimple holonomic $D$-modules, conjectured by M. Kashiwara.
