Kenji Shimizu is one of the last direct students of the O-Sensei. He made his own school and named it Tendoryu Aikido after the death of a founder.
Tendoryu Aikido differs from the other styles in its emphasis on large and clear movements, and its smooth and harmonic flow of motion.
Kenji already had a 4th dan in Judo when he got interested in Aikido. This is another reason why he does have such a clean technique and why he got his 4th Dan in Aikido from a founder after only 4 years of being an uchi-deshi. You may have seen his 1985 movie which is a great presentation to his Aikido.
In 1998 Kenji received his 8th Aikido Dan from the Japanese Budo Federation, not from the Aikikai. This is a way of Kenji Shimizu. He and Shigeo Kamata are the authors of the book Zen and Aikido.
Since 1978, Shimizu has regularly held seminars in European countries like Germany, Holland, Belgium, France, Serbia, Italy, etc. Sensei introduced Aikido to some of those countries and in 2002 he was awarded as a Foreign Minister of Japan for his work spreading Aikido abroad.
Kenta is a son of Kenji Shimizu and they call him Waka Sensei in Tendoryu. Enjoy a Youtube channel with more of them.