What is connecting basic attacks after the 4th attack?
All fighters' basic attacks consist of four attacks. The last 4th attack usually has a long post delay, so you must cancel it with a skill to continue your combo. However, some fighters have a short motion and post delay, so you can connect basic attacks again. By using this, you can deal more damage than general combos.
Unfortunately, this isn't possible with all fighters. Currently, among the 37 fighters, Kyo, Iori, Chizuru, Joe, Kim Kaphwan, Mai, and Orochi Chris can use this technique.
Being cool begins with Oniyaki! "Kusanagi Kyo"
Kyo's 4th basic attack, Oniyaki, has a short motion animation while the opponent gets airborne, so you can connect the 1st basic attack, Aragami. When the opponent is falling from the air, you squeeze in Aragami. Since Aragami doesn't have airborne, standing, or knockdown effects, the opponent can get away by breaking their fall (rolling, dodging) before the 2nd basic attack, Yanosabi, connects. That being said, you need to connect skills after using the 4th basic attack Oniyaki → 1st basic attack Aragami combo to connect following combos.
If Kusanagi can, Yagami can! "Yagami Iori"
Iori's 4th basic attack is also Oniyaki, like Kyo. In Iori's case, you can connect up to two basic attacks. What makes it even better is that the basic attacks of Iori are LP Aoibana attacks from the old KOF versions. The Aoibana (W) is the HP version. Aoibana has the best connections is all of the KOF series, and this stands in KOF Arena as well.
My family is also from the sacred treasures…! "Kagura Chizuru"
Chizuru's family is also from the sacred treasures, like Kyo and Iori — this fact may not be related, but Chizuru can also connect basic attacks after her 4th basic attack. This is because the opponent who is struck by the 4th attack, Tenjin, gets airborne, so Chizuru can connect the 1st basic attack. In this case, the opponent can break their fall and roll away first before the 2nd basic attack connects.
Must-do technique to make up for lacking damage, "Joe Higashi"
Joe can connect up to 2 basic attacks safely after his 4th basic attack. As Joe's skill damage is on the low side, you need to learn the 6-hit basic attack combo to connect the combos into a big hit in actual fights.
Hardest in difficulty, but a big hit if you succeed! "Kim Kaphwan"
Kim Kaphwan has very good basic attacks. After his 4th basic attack, roundhouse upward kick, you can safely connect the 1st basic attack, upward kick. However, there's an issue in connecting skills after the upward kick — if the skill is even slightly late, the opponent can get away by breaking their fall and dodging. This makes the combo connection very difficult. As Kim Kaphwan is considered one of the “weaker” fighters, due to his skill-based fighting style, you have to learn this technique to connect big combos. Without this combo, it's like cutting Kim Kaphwan's ability in half.
Only possible in the corner, "Shiranui Mai"
Mai's attack range of the 1st basic attack (Senzuki + Senda) is short, so you can't connect it in the open after the 4th basic attack (Fuusya Kuzushi) — it can only be connected in the corner. As her main strike skills, Shinobi Bachi (Q) and Ryuuenbu EX (W) can't be avoided by emergency dodge, so you can corner your opponent quite easily. With this, the basic attack connections can be used more often than not in actual fights.
What you have to beware of is that Mai's 1st basic attack consists of two motions. The 1st basic attack consists of Senzuki and Senda — you must cancel Senda after the 1st hit to connect skills. If you connect Senda, the opponent who's airborne from the 4th attack, Fuusya Kuzushi, reaches the ground first, so they can get away by breaking their fall and dodging.
Infinite combo possible, "Orochi Chris"
Orochi Chris can connect infinite combos with 4 basic attacks, 1 basic attack, and skills, so the power of his combo is stronger than other fighters. As his skill attacks make it hard for Orochi Chris to bring the initiative, if you master this technique, you can connect strong infinite combos in any situation.