Wagashi are traditional Japanese sweets.
Here are some wagashi shops in Tsukuba:
2. In Takezono. From Kasumi Gakuen carpark (main one, exit on the Drug Terashima side). Go out of the carpark and turn right. Very soon you will come to an intersection with Hard Off on the left corner. Turn RIGHT. Soon on the left you will see a big building with a skin clinic and beauty clinic on the ground floor. On the far end of the building is a wagashiya. If you get to the next cross street, you went too far.
Sorry, I know these shops but I haven't shopped there. I actually use two different very local shops run by old people that are super delicious but very difficult to find. (One is very far north).
Another choice you might be able to find is one in Namiki. Go along Higashi Odori almost to R354. Just before 354 there is a signal with a kaiten sushi shop on the left and a big Joyo Bank on the right. Turn LEFT. Go down that street almost to the end (the end is a T-junction with 7/11) and one block before the end, you can see signs to say there is a supermarket and shops. Turn left into that street. Soon you will find a supermarket. Just past that is a good wagashiya and next to that is Peter Pan breadshop (Namiki shop).