Style
Under Shinbo, Oishi's style takes derivatives of Shinbo's style as his own, such as Shinbo's usage of faceless "mob" (background) characters. Shinbo made these mob characters faceless, or simply wouldn't include them at all, but Oishi added floral patterns, his name, and other Kanji text on top of those faceless characters, which Shinbo commented was "surprisingly interesting." With the switch from analog to digital in the early-to-mid 2000s, Shinbo noted that Oishi's talent was able to blossom due to the freedoms in creating and switching colors in digital environments. While working on Pani Poni Dash, Oishi attempted to experiment with references to other media, and in one of his episodes tried referencing a drawing of Bakanon's father from Tensai Bakabon by Fujio Akatsuka. However, he was scolded for its inclusion by producers and was told that it might be painted over; though, Oishi instead suggested changing the drawings to flowers, which eventually stuck. Oishi said that he grew up on the works of Osamu Tezuka, which sometimes referenced or outright borrowed drawings from other works, and questioned why Tezuka's works were allowed, but he was not allowed do the same. While Pani Poni Dash series director Shin Oonuma was working in tandem with the rest of the staff on creating references, parodies, and better works, Oishi commented that he worked more alone and away from the Oonuma team. Rather than put in things that other people were suggesting like the Oonuma team, Oishi appealed more to self-indulgence in putting only what he liked into his episodes, such as references to GeGeGe no Kitarō. Oishi experimented with high-saturating colors and 3DCG background environments as well as the interactions between 2D-animated characters and 3D models. Similar to Shinbo's desire to make "good pictures" in his works,[13] Oishi places a particular emphasis on making images that he believes are the best that he can make.
Oishi experimented with coloring in Hidamari Sketch, which he did art design work for across the series alongside Shaft animator Yoshiaki Itou. According to Oishi, Shinbo's orders for the style of the work included limited range of camera "angles" and positioning for the Hidamari apartments and the individual rooms of the main characters. He at first struggled in creating a style that met Shinbo's orders, but eventually decided upon bright colors and ensuring that photographs could be inserted with ease and that light objects could be shown with light lines. In designing the color schemes for each of the character's rooms and their motifs, he paid most attention to the color balance.
Oishi has also become particularly well-known for his use of on-screen text, a style that Oishi overall contributed to the house "Shaft style" originating in the Pani Poni Dash openings. In the midst of episodes themselves, however, the initial appearance of on-screen text as it appears in Shaft series aside from episodes or series directed by Oishi comes from Hidamari Sketch episode 2, in which he used Kanji to punctuate or emphasize lines of dialogue for comedic purposes, for puns, and so forth. Later, Shinbo asked Oishi to be the series director for Bakemonogatari with the intent of visualizing words themselves, which Oishi had proven himself to be good at doing. However, as Oishi experimented more with on-screen text, and its usage was incorporated by the other Shaft directors, so too did its incorporation by Oishi himself.
Discussing the differences between Oishi and Itamura as the series directors of Monogatari, sound director Youta Tsuruoka opined that Oishi was an "intuitive" director in contrast to Itamura's "logical" approach.
