[1] Hasegawa learned English during his school years, and together with three friends, formed an art club known as the Hakuzōkai (White Elephant Group).

[5] Hasegawa helped reorganize a prominent oil painting exhibition society as the Jiyū Bijutsuka Kyōkai ("Free Artists Association") in 1937.

After his short jail sentence, Hasegawa moved his family to Nagahama, north of Kyoto, where they spent the rest of the war in extreme poverty.

During this time, Hasegawa began subsistence farming and all but stopped creating artwork or writing art essays.

[10] In the early 1950s, Hasegawa completely abandoned oil painting and began creating works using traditional Japanese materials, including ink, paper, and woodblock printing.

Hasegawa and Noguchi visited landmark sites together including the Katsura Imperial Villa, Ryōan-ji, and Ise Shrine.

[16] Hasegawa played an important role in spreading the teachings of Zen to the artistic community in San Francisco, notably to the Beat poets.

By the mid-1930s, when he first became involved with the Free Artists Association, Hasegawa's work was transitioning into abstraction, and he began experimenting with collage using materials such as yarn and glass.

[5] After the war, Hasegawa's paintings of the late 1940s began to explore imagery from prehistoric Japanese art, including artifacts from the Jōmon, Yayoi, and Kofun periods.

This was a form of primitivism and Orientalism but specifically focused on Japanese culture, and was largely inspired by his "Old Japan and New West" theory.

His interest in prehistoric Japan resonated with the postwar work of other Japanese artists such as Tarō Okamoto, who was also examining ancient artifacts but was largely inspired by the primitivism of Parisian modernists.

Some of his ink paintings from this time closely approached avant-garde calligraphy practiced by calligraphers such as the members of the group Bokujinkai in the 1950s.

Avant-garde calligraphy focused on the form of ink lines but often resulted in abstract art rather than conveying any legible characters.

[24] Hasegawa first encountered experimental photography and photograms through European and American magazines reproducing works by artists such as Man Ray and László Moholy-Nagy.

[25] His first photographic works were in the documentary tradition, taken during his trip to China in 1938, where he composed experimental shots of Buddhist cave sculptures.

From 1953 to 1954, he created a series of collaborative works with the photographer Kiyoji Ōtsuji and other artists from Jikken Kōbō for the Asahi Picture News.

At the same time, he published numerous articles on Japanese artists including Tawaraya Sōtatsu, Narashige Koide, and Ike no Taiga.

Since the 1930s, many of his writings probed the intersections between "Old Japan and New West," with articles including "Letters from France and America" (1951), "Making Katsura Imperial Villa Abstract" (1951), and "Calligraphy and New Painting" (1951).

Hasegawa also contributed several articles to Bokubi in which he theorized (as he had in the 1930s) a particular relationship between abstract painting and calligraphy, including a series entitled "Reflections on New Western and Old Eastern Art.

[27] The parallels Hasegawa discussed between Western abstract art and Japanese calligraphy deeply inspired the calligraphers of Bokujinkai and contributed to their early theoretical foundations.