Cursing people by sabotage (physically) would probably do less harm or the least minor injury like larceny.
However cursing other people through black spells just because they have done something worse to you would bring calamity in terms of the users might be receiving retributions.
Black spells are something normal humans are unable to see.
Poor mana, its not entirely her fault in the 1st the place as it was her friend Miyabi who insisted & installed the Curse Apps by Nanashi & Kubire Oni!!😣😣