Making his first appearance in Chapter 49 of the manga (Volume 9), Manabe appears at first as a rather lazy, yet outgoing and joyful young man, and has not changed since. Acting as Vice President of Kaibara High School's student council, Kakeru is "second-in-command of the School's Defense Force" and more than passionately works to be one of what he thinks is a Super Sentai type of job, often stating that he's "Black" (as in the black Goranger) while Yuki is "Red" (the leader). Manabe can also be described as a younger version of Ayame Souma (whom Manabe, upon meeting, immediately hugged and said no other person would be fit to be the Defence Force's commander), Yuki's older brother, and often is seen having striking similarities in personality. Yuki also compares him to Kyou with his ability to make friends.
Though he might appear constantly happy and joyous on the outside, Manabe actually at times looks down on himself, and can often get serious if he sees the need to.
Manabe is always fascinated by the Souma family's beauty, as he is occasionally seen asking different Souma family members their secret to their handsomeness.
Manabe is also the half-brother of Machi Kuragi, the quiet and pensive treasurer. He is very protective of her and can often be seen ordering her around, though rather out of love than sibling superiority. They share the same father, but have different mothers. According to Kakeru, he is the illegitimate son of their father, but because he was older than Machi and the only son, their mothers got into a heated dispute as to who was to be their father's heir. Machi's mother was particularly hard on Machi, forcing her to be as perfect as possible, so that as the legitimate child of her father, she would become the family's heir over Kakeru. The matter was settled when Machi's younger brother was born and Machi was brushed aside. As a result, Kakeru feels he needs to take care of his younger sister given that he feels she has been treated unfairly and she has become unloved. Manabe tells Yuki at one point that he himself noticed how stupid the inheritance dispute was and told his mother that he would not take part in it. He'd go on a rampage and shout the words, "I'm not gonna play your stupid game anymore!." Which soon made his mother realize that he was right. He told Yuki that this made him "officially free." He also said "maybe that means Machi hasn't gained her freedom yet."
Although Machi and her mother still need to work things out, Kakeru and his mother seem to get along fine, though they argue regularly about trivial matters very loudly, which results in complaint from the landlord. Kakeru's mother seems to have decided that she doesn't care about the inheritance anymore.
Due to his vice presidential status he is also very acquainted to Yuki Souma, the student council president. Together the two, although their differences are quite obvious and their personalities at times clash with one another, have developed a rather bonded relationship and the two are now finally seen smiling together in some parts of the manga, rather than Manabe just teasing Yuki, or falling asleep while Yuki is talking.