Kakizaki Masasumi made his debut in Bessatsu Young Sunday in March 26, 2001 with a oneshot named Two Tops (ツートップ). Later that year, he made his first serialization in Weekly Young Sunday with X-Gene manga as illustrator together with Kentaro Fumizuki (story). X-gene is about a few chosen people, whose DNA contains genes from certain unique animals that can turn them into that animal and receive its attributes. The manga continued from Issue 45-2001 to Issue 28-2002, spanning 3 volumes. In September 16, 2001, he made another oneshot in Bessatsu Young Sunday named Teppeki D (鉄壁D).
In 2002 he teamed with ABE George and started new serialization in Weekly Young Sunday Issue 51-2002 with Rainbow: Nisha Rokubou no Shichinin (RAINBOW 二舎六房の七人). The manga was set in the 1950s and focuses on six junior delinquents aged sixteen to seventeen that are sent to the Shounan Special Reform School. They learn to cope with the atrocities and unfairness they encounter there. The manga continued in Weekly Young Sunday until Issue 17-2008, after which was moved in Big Comic Spirits in Issue 29-2009 and continued until Issue 5-6-2010, spanning total of 22 volumes. In 2005 Rainbow won in the general category of the Shogakukan Manga Award. It was also made into 26 episode anime in 2010 by Madhouse.
In September 26, 2008, he started a new serialization in Big Comic Superior with the manga Kansen Rettou. The story is about a new deadly virus, who wipes out big part of the population for a short time. The manga continued until January 1, 2009, and spanned 1 volume.
In 2010, he started a horror story in Big Comic Spirits Issue 28-2010 named Hideout and continued until Issue 38-2010, spanning 1 volume. The story is about a man, who decides to start new life, after he kill his wife.
In February 9, 2011, he created 2 part oneshot in Weekly Shonen Sunday named Toujuushi (Bestialious) (闘獣士(ベスティアリウス)). Set in the Roman empire, where a young gladiator was trained by the last wyvern.
In 2011, Kakizaki started a new manga in Weekly Young Magazine Issue 28-2011 named Green Blood. The manga is about two young men who grew up in the Five Points: one, a gangster hitman; the other, a boy who hates the gangs. The manga ended May 13 2013 after several hiatus, spanning 5 Volumes.
In August 2013, Kakizaki started a new series about roman knight story in Issue 36-37 2013 in Weekly Shonen Sunday. The manga is named Toujuushi Bestialious and is based on the oneshot he made in 2011 with the same name.