Arata Haitani (灰谷新, Haitani Arata) is a supporting character in the Sekai-ichi Hatsukoi series. He is the editor-in-chief of Shuudansha's Weekly Earth manga magazine. He used to work with Masamune Takano, and he currently works with Ritsu Onodera's ex-colleague Saeki.
He refers to Ritsu as "The Famed Heir to the Empire" because of Ritsu's family. Haitani and Ritsu have close relations due to them both knowing Takano and Saeki. Ritsu has been forbidden to see him again, since Takano is scared that Haitani will "steal" him. Haitani seems to have feelings for Ritsu, as in Chapter 20 of Ritsu's story, but these appear to be lies. Haitani asks Ritsu out and confesses to him, saying he's "serious about him". Ritsu hasn't yet officially rejected him; he wanted to tell Haitani he had somebody that he loved, but Takano interrupted him before he could do so.
Haitani and Takano were co-workers back at Shuudansha in the Weekly Earth department. Takano "stole" Haitani's previous lover, as the lover had feelings for Takano. Takano did turn him down, but the lover dumped Haitani. This caused Haitani to mess with Takano, such as "stealing" Takano's current girlfriend at the time, and making his job difficult, which lead to Takano quitting. Haitani is still seeking revenge for what Takano did.
The reading of his name "Arata Haitani" is confirmed on the back cover of volume 8.
This character is commonly referred to as Shin Haitani instead of Arata Haitani among English-speaking fans. This is because his name was first seen written on his business card with no furigana (pronunciation), and Shin is one way of reading his name, which was picked up by fans.