Hopefully this changes up the revenge isekai trope. Only lasts 4-5 chapters his whole revenge and gain strength is actually delusions from a mixture of immense pain and mental magic cast by his cousin. Turns out it's all just a dream he was giving himself to ease the pain but cracks in "reality" start to form for him, his magic fails at inopportune times due to his real body failing to maintain the dream world, etc. It all ends with a 6 year old who looks like he lived a marathon through every corpse party or Junji ito story.