Daichi and Hina are the children of Yumi, who is the sister of Akira and Takeshi's father, Hiroshi. Hence, Daichi and Hina are Akira and Takeshi's cousins. 

Yumi, being Hiroshi's sister, is Akira's aunt. Since Kenji is married to Yumi, he is Akira's uncle by marriage. Therefore, Kenji is also Takeshi's uncle by marriage.
Akira has a brother named Takeshi. Their father, Hiroshi, has a sister named Yumi. Yumi is married to Kenji, and together they have a son named Daichi and a daughter named Hina. How are Daichi and Hina related to Akira and Takeshi? Also, commenting on Akira's relationship to Yumi, what would that make Kenji's relationship to Akira? Provide a very short response.