This one needs to go back to the origins of the Japanese language. Although there is no connection between the origins of the Japanese language and the Chinese language, the Japanese language, which is used for writing, has been passed on entirely from China itself. In his book "The Oriental Way of Thinking", the famous Japanese professor from the University of Tokyo, Gen Nakamura, argues and confirms that the Japanese language originated in ancient China.

The original text of "The Oriental Way of Thinking": The Chinese language was introduced to Japan about 1400 years ago. However, until the Tui Ku dynasty only a small group of specialists used Chinese, and they had little influence on the local language. It was only with the beginning of direct Chinese contacts and the introduction of the cultural system of the Sui and Tang dynasties that the number of people learning Chinese and knowing Chinese greatly increased.

In other words, Japanese is very different from Chinese, but Japanese writing, indeed, uses Chinese characters, or the radicals of Chinese characters.

In ancient China, Chinese characters were written from the top to the bottom and then from the right to the left.

So Japanese became written in the same way in ancient times.

In modern times, both Chinese and Japanese have abandoned the right-to-left, top-to-bottom style of writing and replaced it with a left-to-right, then top-to-bottom style of writing.

Manga emerged after this change in writing style, so that "manga" was read from right to left (images and bubbles) and appeared in a variety of writing styles.