This one was a tough one, and might be kind of a stretch, but this week's Tsundere falls more into the realm of a "really well developed character that happens to have a few Tsundere traits" but deep down she is still a Tsundere. She is Isoyama Yomi from the anime Ga-Rei ZERO.
Notice I say the anime, and not the manga, because the Yomi in the Ga-Rei manga is quite a different creature then her prequel counterpart, and also part of why it makes her so hard to define.
Yomi goes through many transformations in personality before Ga-Rei Zero begins, during, and even after it ends. I can think of only a few examples in modern anime where a character has fallen so hard to "the dark side", with such a beautiful young vibrant character turn into one of the most blood thirsty creatures in modern entertainment. She is compelling, and heartbreaking to watch.
Most of the series she is seen hanging around her "sister" and protege, Kagura. They have a borderline yuri relationship, but to Kagura she shows only deredere and no tsuntsun.
Her fiance, Noriyuki, and her attitude towards him are where her Tsundere traits shine to their fullest. In public they are outright violent and hostile towards each other, but when he is able to get her alone, they are both affectionate to one and other and clearly deeply in love.
My reasons for picking her as the Tsundere of the week is slightly dubious as I want to raise more awareness of Ga-Rei ZERO. I realize it is a fairly well known series, but it came out in a year against a bunch of heavy hitters, and I'm sure there were a lot like me who passed up this true gem of a show. A lot of people are decrying the "end of anime", but it is shows like this and Bakemonogatari that I feel will find a new path for anime to take. It throws out a lot of conventions we are used to in anime series and creates something new and unique. Outright tragedy is something that isn't explored enough in character drama in anime.
Most people will also agree that the Manga industry is fine, and that there is a ton of good manga, compared to the not enough good anime. Ga-Rei Zero makes the manga infinitely better. It is a companion piece to the manga, and if you haven't read the manga I HIGHLY suggest you watch Ga-Rei ZERO first, and then read the manga. They are very different in terms of narrative, but they go hand in hand and result in leaving a lingering eerie feeling as you read and know all the tragic pasts of the characters who survived.
I got off on a tangent there, but I hope it helps to emphasis the power of this amazing character. Please Japan, we need more shows and characters like this. And if you have put off watching Ga-Rei ZERO, stop what you are doing and go watch it now.