Yuriko Ishizaka XL (Jagaaaan)

Yuriko was the girlfriend of the main character and wanted to start a family before she hit 30. Although she figured the MC was discontent with life and didn't want to get into a serious relationship, she tried to accommodate him, but he never let it known he wanted a different life. This bubbles over when a mutation caused by otherworldly entities twists Yuriko's desires causing her to gain powers but become erratic. She frustratedly strangles the MC as she begs for him to propose to her. On the verge of death, the MC (who was recently mutated but has full control) uses his powers to blast Yuriko in the stomach, leaving nothing but her dismembered head.