  We introduce the response function (RFs) approach to model the weak lensing
statistics in the context of separate universe formalism. Numerical results for
the RFs are presented for various semi-analytical models that include
perturbative modelling and variants of halo models. These results extend the
recent studies of the Integrated Bispectrum (IB) and Trispectrum to arbitrary
order. We find that due to the line-of-sight (los) projection effects, the
expressions for RFs are not identical to the squeezed correlation functions of
the same order. We compute the RFs in three-dimensions (3D) using the spherical
Fourier-Bessel (sFB) formalism which provides a natural framework for
incorporating photometric redshifts, and relate these expressions to
tomographic and projected statistics. We generalise the concept of $k$-cut
power spectrum to $k$-cut response functions. In addition to the response
function for high-order spectra, we also define their counterparts in real
space, since they are easier to estimate from surveys with low sky-coverage and
non-trivial survey boundaries.
