If there was an anime of this then it’ll reach top 10 saddest anime where all your friends died as you keep on living until you find no purpose to continue living.
@ReRead In a couple weeks (April 10th is the premiere) there's gonna be an anime with almost this same sentiment. Called "I've Been Killing Slimes for 300 Years and Maxed Out My Level"
the LN at least starts out with the MC being Isekai'd as a witch and when she realized that all the people she knew died she became a recluse for 300 years to spare her from forming relationships with anyone