Early career Kennedy played
high school football at the prestigious in
Aomori, where he was scouted by many J.League clubs. Kennedy progressed both junior high and high school at Aomori between 2015 and 2018. In his first year at Aomori Yamada, he helped the school win the National Junior High School Soccer Tournament Final in 2015. Together with teammates
Riku Danzaki, they were one of the key players to win the Outstanding Player Award of the tournament. Having started out as a striker, Kennedy began playing as a
center back in his third and final year of high school. In 2018, Kennedy helped the Aomori Yamada win Sanix Cup International Youth Tournament and National High School Soccer Championship Final. Following this, he was included for the National High School Soccer Championship Outstanding Player. Throughout 2018, his performance at Aomori Yamada, once again, was noticed by Gekisaka, who described him one of the players to watch.
Avispa Fukuoka It was announced on 18 July 2018 that Kennedy would be joining
Avispa Fukuoka ahead of the
new season. He was given the number 20 shirt by the club. Kennedy made his Avispa Fukuoka debut, starting the whole game, in the opening game of the season against
FC Ryukyu but he conceded three goals, as the club lost 3–1. In a follow–up match against
V-Varen Nagasaki, Kennedy made an improvement in his second appearance for Avispa Fukuoka when he helped the club kept a clean sheet, in a 0–0 draw. After missing two matches due to an injury, Kennedy returned to the starting line–up against
Albirex Niigata and kept another clean, in a 2–0 win on 23 March 2019. He was given a first team chance under the management of
Fabio Pecchia. In a match against
Zweigen Kanazawa on 3 May 2019, Kennedy received a red card for a second bookable offence, in a 1–1 draw. He previously played uncharacteristically, such as, losing possessions and giving away the ball that saw him substituted at half time, in a 1–1 draw against
Yokohama FC on 7 April 2019. After two months away, Mikuni made his first appearance for Avispa Fukuoka, playing 120 minutes, in a 2–1 win against
Kagoshima United in the second round of the Emperor’s Cup. At the end of the 2019 season, he went on to make eleven appearances in all competitions. Following this, Kennedy briefly went on an invitational trial with Italian side
Juventus U23 for two weeks. At the start of the 2020 season, Kennedy had his contract renewed with Avispa Fukuoka. After being absent from the first team, he scored on his first appearance of the season, in a 1–1 draw against
Ehime FC on 29 July 2020. This was followed up by setting up an equalising goal, in a 2–2 draw against
Ventforet Kofu. In a match between Avispa Fukuoka and
Mito HollyHock on 4 November 2020, Kennedy played briefly against his older brother,
Stevia when he came on as a late substitute, as the club won 1–0. However, Mikuni made only five starts for Avispa Fukuoka and found his playing time from the substitute bench. Despite making nineteen appearances and scoring once in all competitions, he helped the club promoted to
J1 League. Ahead of the 2021 season, Kennedy had his contract renewed with Avispa. On 3 March 2021, he scored his first goal for the club, in a 3–2 loss against
Consadole Sapporo in the group stage of the J. League Cup. Kennedy then made three starts, playing as a striker. Before going on loan to
Tochigi SC in May, he made four appearances and scoring once in all competitions. Following his loan spell, Kennedy made his first appearance of the 2022 season for Avispa Fukuoka, starting a match and played 82 minutes, in a 1–0 loss against
Yokohama F. Marinos on 10 September 2022. After making seven appearances in all competitions at the end of the 2022 season, he had his contract renewed with Fukuoka. Throughout the 2023 season, Kennedy made only twelve starts for Avispa and found his playing time mostly confined to the substitute bench. He then helped the club qualify for the J. League Cup knockout stage after winning the two remaining matches of the group stage against Albirex Niigata and
Kashiwa Reysol. In a match against
Vissel Kobe on 25 June 2023, Kennedy suffered an injury and was substituted in the 39th minute, as Avispa Fukuoka lost 3–0. After being sidelined for three months, he returned from injury, coming on as a 51st minute substitute, in a 2–0 win against
FC Tokyo, as the club advanced to the semi–finals of the J. League Cup. Kennedy played in both legs of the semi–finals of the J. League Cup against
Nagoya Grampus, as he helped the club won 2–0 on aggregate to advance to the final. However, he was left out of the squad in the
J.League Cup final, as Avispa Fukuoka won 2–1 against
Urawa Red Diamonds to win the tournament. At the end of the 2023 season, Mikuni made twenty–eight appearances in all competitions.
Tochigi SC (loan) On 21 May 2021, Kennedy has been loaned out to J2 League side
Tochigi SC for the rest of the 2021 season. Kennedy made his debut for the club, starting the whole and kept a clean sheet, in a 3–0 win against
Matsumoto Yamaga on 23 May 2021. This was followed up by helping Tochigi SC keep two clean sheets in the next two matches. Since joining Tochigi SC, Kennedy started in the centre–back position for the next two months. However, he was dropped to the substitute bench for the rest of the 2021 season after the club went on winless run for three months. At the end of the 2021 season, Mikuni made twenty–four appearances in all competitions. Kennedy had his contract renewed with Avispa Fukuoka and was loaned out to Tochigi SC for the 2022 season. He made five appearances for the club before returning to his parent club on 10 August 2022.
Nagoya Grampus On 25 December 2023, it was announced that Kennedy joined J. League side
Nagoya Grampus on a permanent transfer. He make his debut for the club on 23 March February in a 3–0 lost to
Kashima Antlers. On 21 April, he scored his first goal for the club in a 2–1 win over
Cerezo Osaka. ==International career==