  An inflationary scenario is expected to be embedded into an ultraviolet (UV)
complete theory such as string theory. The effect of UV complete theories may
appear as nontrivial kinetic terms in the low energy effective field theory,
which provides a nontrivial geometry in field space. In this paper, we study
the effect of the geometry of multi-form-field space on an inflationary
scenario. In particular, we focus on the geometric destabilization mechanism
which induces the phase transition from the conventional slow-roll inflation to
a novel inflationary scenario. Anisotropic inflation is a typical example of
the new phase. To conform to observations, we restrict us to isotropic
configuration of form fields. We clarify the conditions for the onset of the
destabilization and reveal the geometric structure of attractors after the
destabilization. We classify the viable models from the observational point of
view. We also investigate the features of the primordial fluctuations and find
the similarity to hyperbolic inflation. By calculating the power spectrum, we
make several phenomenological predictions which are useful to discriminate our
models from others inflation models. We found the scalar-to-tensor $r$ will be
suppressed by large one-form gauge fields, while it has the same order as the
slow roll parameter $r\sim\mathcal{O}(1)\epsilon$ for large two-from gauge
fields.
