What's Wrong with Only Having a Shield? My Summoner Hates Me

Follow the adventure of an ex-university student, Rin, as he gets reincarnated as a "Spirit" with a shield being his only weapon in another world. Although he is overjoyed at the chance to live out a childhood fantasy, there's one major problem... His "Summoner", Isabel, sees no reason to keep a "Spirit" who's only good for defense in her party! Rin has to find a way to survive in battles and dungeons as an unwanted and heavily under-leveled character!