To outsiders Karin appears to be a normal, cheerful high school student. However, Karin and her family are all vampires. To make matters worse, Karin is not even an ordinary vampire - she is a blood maker and must inject the excess blood into her victims! If she doesn't find a victim to bite in time, her extra blood is expelled in the form of a massive nosebleed. Karin's already difficult life is made worse when Kenta Usui transfers into her class and she finds her blood increasing at an alarming rate. When sharing classes and an after school job together make avoiding Kenta impossible, Karin must find a way to keep her rapidly increasing blood under control or risk exposing her family's secret.
The one real similarity between Toradora! and Karin are the male leads. Both of them were raised by a single mother and both of them grew up with the potential to become a housewife...
Considering how common it is in shounen media, you might find if refreshing that neither of those two is a pervert. Both of them care for their woman because they love them rather than because of physical attraction (I'm not saying that there isn't any). What's more, in both cases said love is something that evolves from friendship and takes some time to "hatch".
So if you liked the male lead and romance in one of those two series, the other one should be worth checking out as well.
Those series are probably more different than they are similar, but something tells me that fans of one of them might find the other interesting. In both series the female lead doesn't look her age at all. Even though she is in her late teens, people mistake her for grade-schooler. Here comes the twist, in Toradora! the male lead (her peer) ends up having to take care of her (because she is kind of helpless on her own), but in Friendly Winter the guy (and he is 2 years younger than her) is the one who needs to be taken care of.