Basically it's a part of Japanese culture. Tattoos are associated with Yakuza/crime.Well, I really liked that chap up to the point where Keigo deleted the tattoos. Like, from a narrative point of view, it's fine since the tattoos held no special meaning to her beyond covering her scars, but at the same time it's annoying from a meta point of view since it was most likely done to make her "waifu status" go up for readers, to clean her up.
And here I was, in a previous comment section, going "I appreciate how the author went with a love interest who looks a bit different than the typical waifu with those tattoos she has + kind of wild hairstyle". Oh well.