In the humid summers I seek relief in chilled fruit saké that are tart and mouthwatering. Here are two worth seeking out, lemon and natsumikan (imagine an orange pomelo). My favorite producer for these kajitsushu is Tsuru Ume from Wakayama. Their aromatic yuzushu is also one of the best made in Japan, in my opinion. On the rocks, or served straight, this is an excellent start to any meal, or a refreshing break in the afternoon.
Tsuru Ume also makes outstanding umeshu, which is no surprise as the apricots from Wakayama are a regional specialty.
I love the selection of kajitsushu at Shinbashi’s Oboro Saketen. Okuma-san, the owner, went to college in Minnesota and speaks English. Tell him Yukari sent you.
Interview with Okuma-san of Oboro Saketen.
http://metropolisjapan.com/seasonal-secrets-of-hiya-oroshi/
Oboro Saketen
http://www.oborosaketen.com/page3.html
Minato-ku, Shinbashi 5-29-2 港区新橋5-29-2
Side note – this is a well-stocked sake shop with some hard-to-find sake and shochu. They will ship to your home or hotel with an overnight delivery.
Food Sake Tokyo 
Do you know Kurand Sake Market in Tokyo? There you can try 100 different kinds of sake!
I am familiar with them, but have not been yet. Great concept!