kurihara_kenshirou
Artist.
Japanese name: 栗原 ケンシロウ (Kurihara Kenshirou)
Circle name: 拳王親衛隊 (Ken'ou Shin'eitai)
He is also a member of Bunjutsu Fortissimo, a doujin circle led by fanfic writer Miura Sairasu. Sairasu often uploads the illustrations of other circle members to his sites/accounts with their permissions. The real artist credits are on his Pixiv commentaries.
Miura's accounts:
* Name: 三浦サイラス (Miura Sairasu)
* Circle: 文術フォルテッシモ (Bunjutsu Fortissimo)
* Illustrators: Kurihara Kenshirou and Nonohara Nyorai
* Blog: http://blog.livedoor.jp/sairasu22/
* Pixiv: http://www.pixiv.net/member.php?id=2132505
* Pixiv novels: http://www.pixiv.net/novel/member.php?id=2132505
* Twitter: http://twitter.com/sairasu9