In Japan, manga, anime and even “light novel ” creators all claim early an 20th Century Czech Art Nouveau artist and illustrator as an influence, according to Japanese pop culture blog Ichi-Up .
A foreign illustrator who worked one hundred years ago has influenced Japanese creators in a variety of ways. His name was Alphonse Mucha.
According to Ichi-Up, popular Japanese creations including Record of Lodoss War (ロードス島戦記 ), Video Girl Ai (電影少女 ), GOSICK  and Gundam are all influenced by Alfons Mucha  (1860-1939, known in English as Alphonse Mucha). His influence frequently surfaces elsewhere in Japanese pop culture as well.
— 藤原カムイ (@kamuif) July 27, 2019 
[…] A new series of Dragonquest will be released shortly. Look for the comics featuring an Alphonse Mucha-esque portrait of Rubisu! […]
A reason for Mucha's influence on contemporary Japanese culture can be found in the Art Nouveau  movement, of which Mucha was a part, which was itself influenced by the Japonism  fad that swept the European art world in the late 1800s:
The name ‘Art Nouveau’ comes from the name of an art gallery in France (sic). The Art Nouveau art gallery was supportive of Japanese art, particularly Japanese ukiyo-e prints and crafts, as well as the works of (European) artists who were influenced by Japan.
Markéta Hánová the Czech National Gallery's Director of Oriental Art Collections notes  (in French):
Du fait d’avoir vécu à Paris, Mucha était aussi influencé par le style d’art japonais. Sur ses affiches, nous pouvons voir le motif de l’iris qu’il faisait en très grand. On peut voir à travers ces iris comme à travers une grille un autre objet à l’horizon, c’est une composition très typique des estampes japonaises.
Having lived in Paris, Mucha was also influenced by the Japanese art style. On his posters, we can see he made the pattern of the irises (in this illustration ) quite large. We can see through these irises as through a grid another object on the horizon — a very typical composition found in Japanese prints.
Besides anime, manga and light novels, Mucha pops in up in other parts of Japanese culture as well:
— ゴフクヤサン：デジタル捺染のオリジナル生地を使用した浴衣や帯を販売しています。 (@gofukuyasan) October 23, 2018 
A black crepe ‘haori’ (traditional Japanese long kimono-style jacket) where the ‘haora’ (a hidden pattern on the inside of the garment) features an Alphonse Mucha design. […]
In the Czech Republic, Mucha and Art Nouveau's influence on Japanese creative culture is still remembered and celebrated. In 2014  there was a large exhibition in that country about Japonism among Czech visual artists, including Mucha.
Besides his ongoing influence on Japanese pop culture, Japan is also home to one of the largest collections of work by Mucha in the world as part of the Ogata and Doi collections at the Sakai City Museum , near Osaka in western Japan.
Currently, Mucha's works are display in Tokyo at Bunkamura until the end of September, 2019. The exhibit, “Timeless Mucha: The Mucha to Manga — The Magic of Line “, features not only a number of Mucha's illustrations, but also a range of works by artists who were influenced by Mucha. Organized by the Mucha Foundation , the exhibition with tour various cities  throughout Japan in 2020.