If you're looking for manga similar to 13, you might like these titles. All recommendations are made by Anime-Planet users like you!
Fumio is a woman scorned. She’s alienated from her dear friend Kaoruko, but more importantly the love of her life, Takumi, appears to have fallen for a new transfer student at school. Upset and realizing that she can’t live without him, she does the only logical thing: she gets her chainsaw, builds up her resolve, and goes to kill both him and herself...
Lead girl, check. School setting, check. Interesting weapons of choice for a school setting, check. Both are hilariouly entertaining shorts that will make you turn the page so fast to see what happens next. Revenge is always an interesting thing in Japan.