sci-misc/gri-2.12.13 depends on app-text/ghostscript-esp but should depend on virtual/ghostscript. The different ghostscript implementations block each other since virtual/ghostscript became stable. Depending directly on ghostscript-esp is very likely not necessary for gri.
*** Bug 158381 has been marked as a duplicate of this bug. ***
Please read the ebuild (especially the comment on ghostscript there).