First Super Lightweight Grand Prix

On September 5, 2014, it was announced that Kaew would be one of eight participants in the one-day K-1 Super Lightweight World Grand Prix, which was held on November 3, 2014, and would face the reigning Krush Lightweight titleholder Hideaki Yamazaki in the tournament quarterfinals.^[3] He won the fight by a narrow unanimous decision, with all three judges awarding him a 30–29 scorecard.^[4] Kaew advanced to the semifinals, where he faced the two-time Krush Grand Prix winner and former welterweight champion Yuta Kubo. He floored Kubo with a right hook at the 1:52 minute mark of the second round, which left the Japanese fighter unable to rise from the canvas.^[5] Kaew faced Yasuomi Soda in the tournament finals and was able to overcome him by majority decision, with scores of 30–28, 30–29 and 29–29.^[6] Kaew dedicated his win to his father, who died a week before the tournament.^[7][8]

Title defenses

Kaew faced Minoru Kimura at K-1 World GP 2015 -60kg Championship Tournament on January 18, 2015. He lost the fight by majority decision.^[9] Kaew returned to muay thai to face Kenta Yamada at WPMF JAPAN×REBELS SUK WEERASAKRECK FAIRTEX on March 22, 2015.^[10] He won the fight by unanimous decision, with scores of 49–47, 49–48 and 50–48.^[11]

After beating Zhang Chunyu by unanimous decision at Kunlun Fight 26 on June 7, 2015, Kaew was booked to face Yasuomi Soda in a rematch at K-1 World GP 2015 -70kg Championship Tournament on July 4, 2015. He was more successful than in their first meeting, as he won the fight by unanimous decision, with all three judges scoring the bout 30–26 in his favor. Kaew knocked his opponent down with a one-two near the end of the second round.^[12]

Kaew made his first K-1 Super Lightweight title defense against Minoru Kimura at K-1 World GP 2015 The Championship on November 21, 2015.^[13] He avenged his first loss under K-1 rules with a first-round stoppage of Kimura.^[14] Kaew made his second title defense against Massaro Glunder at K-1 World GP 2016 -65kg Japan Tournament on March 4, 2016. He won the fight by split decision. Two of the judges scored the bout 29–28 in his favor, while the third judge had it scored 28–27 for Glunder. Both fighters were deducted a point in the second round for excessive clinching.^[15] Kaew next faced Ilias Bulaid in a non-title bout at K-1 World GP 2016 -60kg Japan Tournament on April 24, 2016.^[16] He won the fight by unanimous decision, with a 30–29 score on all three scorecards.^[17]

Second Super Lightweight Grand Prix

Kaew was announced as one of eight participants in the 2016 one-night K-1 Super Lightweight World Grand Prix, which took place on June 24, 2016. He faced the inaugural Krush Super Lightweight champion Hiroya Kawabe in the quarterfinals.^[18] Kaew needed just 36 seconds to knock Hiroya out with a well place left hook, which earned him a place in the semifinals opposite Masaaki Noiri.^[19] He beat Noiri by unanimous decision, with two scorecards of 29–28 and one scorecard of 30–29.^[20] Kaew faced Ilias Bulaid in the tournament finals, having already overcome the Enfusion champion by unanimous decision two months prior. He was even more convincing in the rematch, as he stopped Bulaid by technical knockout in the second round.^[21]

Title loss

Kaew made his Wu Lin Feng debut against Wang Pengfei at Wu Lin Feng 2016 World Kickboxing Championship on January 14, 2017. He knocked Pengfei down once in the third round, en-route to winning the fight by unanimous decision, with scores of 30–26, 29–27 and 29–27.^[22] Kaew made his third K-1 Super Lightweight title defense against the 2016 K-1 World GP 2016 -65kg Japan Tournament winner Hideaki Yamazaki at K-1 World GP 2017 Super Bantamweight Championship Tournament on April 22, 2017. He won the fight by unanimous decision, with all three ringside officials awarding him a 30–28 scorecard.^[23]

Kaew made his fourth championship defense against Masaaki Noiri, who he had previously beaten by unanimous decision in the semifinals of the 2016 K-1 Super Lightweight World Grand Prix, at K-1 World GP 2017 Super Middleweight Championship Tournament on June 18, 2017. He lost the fight by a close and controversial split decision, after an extra fourth round was contested.^[24] Combat Press would later name the bout their "2017 Robbery of the Year", stating: "...during the first three rounds, it appeared that Kaew would retain his title... In the fourth and final frame, it once again looked like Kaew had done enough to win".^[25]

Third Super Lightweight Grand Prix

After suffering his second K-1 loss, Kaew faced Liu Wei at Hero Legend 2017 on September 17, 2017. He won the fight by a second-round technical knockout.^[26] Kaew returned to K-1 to face the 19-year old Ren Hiramoto at K-1 World GP 2018: K'FESTA.1 on March 21, 2018. He lost the fight by a second-round knockout,^[27] in what was later named by Combat Press as their "2018 Upset of the Year".^[28] Kaew's bad form continued into his next appearance as well, as he suffered a unanimous decision loss at the hands of Qiu Jianliang at Glory of Heroes 31 on May 26, 2018.^[29]

On September 4, 2018, it was revealed that Kaew would take part in the 2018 K-1 Super Lightweight World Grand Prix as well, which took place on November 3, 2018, and would face the K-1 WORLD MAX 2010 Lightweight Japan Tournament winner Tetsuya Yamato in the quarterfinals.^[30] He stopped Yamato with a head kick, 92 seconds into the opening round.^[31] Kaew advanced to the penultimate bout of the one-night tournament, where he faced Yasuomi Soda, who he had beaten twice already. He won the trilogy fight by unanimous decision, after an extra fourth round was contested.^[32] Kaew captured his third Grand Prix title after he overcame Daizo Sasaki by unanimous decision in the finals, with two scorecards of 30–29 and one scorecard of 29–28.^[33][34]

Title loss

Kaew made the first title defense of his second title reign against Rukiya Anpo, who entered the fight on a three-fight win streak, at K-1 World GP 2019: Super Bantamweight World Tournament on June 30, 2019.^[35] Anpo initially missed weight by 150 grams at the official weigh-ins, although he was able to make the mark on his second attempt.^[36] The fight was ruled a majority decision draw after the first three rounds, with two judge seeing the fight as a draw, while the third judge scored it 29–28 for Anpo. Kaew lost the fight by unanimous decision after the extension round was fought. He was deducted a point in the fourth round for pulling down on Anpo's head.^[37] Combat Press would later name the bout their "2019 Robbery of the Year".^[38] An immediate rematch took place at K-1 World GP 2019 Japan: ～Women's Flyweight Championship Tournament～ on December 28, 2019.^[39] Anpo was once again declared the winner by unanimous decision, after an extra fourth round was fought.^[40]