Valentine's cards from
Nana's Everyday Life. (TW for if you decide to read it:
CSA (not graphically shown nor sexualised, it's not that kind of publication), child abuse, child abandonment, torture, injury including one that results in disability, homelessness, murder, discrimination, bullying and all around feels, it's a great webcomic but fucks sake it's dark and sad. also at the beginning it treats itself like a joke however becomes more serious rather quickly, so if you dislike such matters being portrayed non-seriously or joked about then keep that in mind, however also keep in mind that it quickly stops joking about such things too)
It's also a fan work of Elfen Lied and contains characters from Gunslinger Girl, however it changes a lot so one does not need to have seen the source materials to understand it, and as a matter of fact I had only heard of either of them via this comic after I had already read the whole thing.