It's a short and to the point manga starring none other than the deadliest sniper in history, Simo Häyhä, gender-flipped for the moe fanbase. The story revolves around the titular White-Witch (or White Death, as he was originally known to the Soviets) and her exploits during the 3 month Winter War from late 1939 to early 1940. This is a short manga numbering about half-dozen chapters and rather straightforward.
The artwork is great, but everything else is lacking. Characters have no depth, plot is simple, and while I did enjoy reading it (mostly for the art), it ended too abruptly and on an unsatisfactory note.
Now, I do note that some are offended by a gender-flipped version of Finland's national hero, but come on now, is this even anything new. Look at the entire Fate franchise, and remember how many times they flipped Three Kingdom characters? I'd say get used to it, because there are a lot more where that's coming from.
Lastly, on a side note, the real Simo used a Model 28 Finnish reworked Civil-Guard Mosin Nagant with a hex receiver, but the version in the manga depicted one with a round receiver. A very notable mistake who knows anything about him and his weapon of choice.