Alternate Title: "Fire-Forged Harem 4P; OpPai, CreamPie, RedemPtion, And The Final Boss Is TraP Yaoi."
Actually; Mari/Kagari isn't really the main "final boss." It's actually Misaki; the woman who dumped Takao, was promptly killed by him due to his rage, and is now a "vengeful spirit."
Also a sub-plot about dads not being there for you then finding out that they're dead. That type of subplot actually hits home for me because my dad wasn't there for 90% of my life... ...and yet I've lived longer than him. ;_;