You might lose your appetite during the hot summer and have lots of cold drinks with ice constantly. This could cool your organs, weaken your stomach and cause water retention. 

Tomato and Tofu Miso soup - this is one of my favorite summer miso soup and a perfect combination for relieving summer-related symptoms such as poor appetite, thirst, and constipation due to excessive heat in your stomach. Tomato promotes body fluid, moistens your body and gives you a sweet-sour taste which increases your appetite.
 Tofu is also a Yin nourishing food, clears excessive heat in your body and eliminates toxins.

Lots of summer vegetables clear heat in your body, quench thirst and help you strengthen your stomach. Also some of them are beneficial for reducing water retention.
As summer vegetables are mostly cool/col-nature food and miso paste is warm-nature food. having good balance is very important in Yakuzen.