He is voiced by Kazuya Nakai in the Japanese version of the anime and J. Michael Tatum in the English Version.
Doumeki is depicted as a tall young man with a serious disposition. It is pointed out several times by Watanuki and those trying to annoy Watanuki, that Doumeki is quite a bit taller than him. He has short dark hair and a narrow face. Because of his personality his face rarely displays any emotions other than anger, though occasionally a smirk does appear. Once in the series he does actually smile but Watanuki quickly tells him it is creepy. In the manga his eyes are more of a golden color but in the anime they appear to be a dull green. He is often shown with a bow which he uses to defend against spirits. His clothing generally consists of his school uniform which is a simple black set of pants and a high collared shirt, the clothing worn for his archery club which consists of a loose white shirt and dark blue hakama (a type of pants), and sometimes a kimono. Later in the series when his grandfather is introduced, it is shown that they look almost identical. The main difference between the two (pointed out by Watanuki) is that Haruka tends to smile much more.
Doumeki's personality is the complete opposite of Watanuki's: cool, calm, rather serious and often sarcastic (which catches the attention of many females in the series). He barely speaks unless explaining folklore or asking Watanuki for impossible bentô lunches (such as ones that contain food that is out of season or hard to find). When talking trying to get his attention, Dômeki often calls Watanuki "Oi". He also has a deadpan sense of humor that is often dark and somewhat cynical.
Much to the annoyance of Watanuki he seems to pop up everywhere, especially when Watanuki gets a chance to be with Himawari (though it is later revealed that this is intentional). He often replies in a one word phrase like "Hn" or "Oh". He is also very observant. Even though he does not often show it, he seems to care for and be very protective of Watanuki, for example when he stands in the rain for hours digging for Watanuki under a bush or when he gives up a significant amount of blood to prevent Watanuki's death.