I Only Have Support Skills - Chapter 15: Main Quest: Track Down Lucius.

This is a story about the protagonist getting the system, going crazy in the biochemical apocalypse, producing aircraft and tanks, destroying zombies, saving good people and killing bad people.

- Description from novelbuddy

"Marry me. Once we're married, I will be loyal to you for life—as long as you keep me alive." Qiao Jiusheng was pushed into the water by her older twin sister, had her identity stolen, losing her old love and life. With no other choice, she seeks out Fang Yusheng, the blind man rumored to have no interest in women. With blank and empty eyes, he says, "Sure." In her past life, she was betrayed by her sister and trapped in the basement. Her tongue was cut off as she watched her sister take her place, winning overall her loved ones, marrying her lover of six years, and starting a family with him. Now that she's back to a time before it all went wrong, Qiao Jiusheng escapes from the river and goes to her boyfriend's older half-brother. She puts on a mask and marries him, to fight their common enemy. The wheels of fate begin to spin, and the severed threads of destiny are once again entwined... Before their wedding, he tells her, "Don't peek at me so openly just because I'm blind and can't see you." On the night of their wedding, he tells her," You don't have to dress like a bear. I don't care for women." Half a year after their wedding, just because she gives another man another look, Fang Yusheng covers her laptop, phone, bedside drawers, desk, and wallet with nothing but his selfies.

After 2000 years has passed, the ruthless demon lord has just been reincarnated! But his aptitude at an academy for nurturing candidates for demon lords is, “Inept”!?

I finally managed to kill the demon lord.