Lantis
Lantis is Zagato's younger brother, which comes as a surprise to the Magic Knights when they return to Cephiro in the second season. His official title is "Cail" and it was his duty to protect Emeraude. Like his brother, he is a powerful magic wielder, but he is a magic swordsman which seems to be an unusual combination in Cephiro. He was Guru Clef's most gifted student in the magic arts. Lantis is voiced KOSUGI Juurouta, Zagato's voice actor. Lantis left Cephiro at some point before the girls' first arrival. He shared Zagato's concern about the pillar system. He went to Autozam, where he and Eagle Vision appear to have formed a close friendship - just how close is teased at, but never discussed in either the anime or manga. Lantis has feelings for Hikaru, but is very much the "strong, silent type" and isn't good with verbalizing his emotions.
Primera
Primera is a cute, tiny pixie who is Mokona's companion/constant antagonist in the second season. She was rescued by Lantis from a monster in the forest, and, naturally, fell for his tall, dark and handsome charms. The size difference doesn't matter to her - she is completely devoted to Lantis. Primera and Mokona are the comic relief in the second season, with Mokona picking on her good-naturedly (like he did with Umi). Primera is the only pixie or fairy we get to see in Cephiro, but the other Cephirans don't seem surprised that pixies exist. She immediately recognizes Hikaru as a rival for Lantis' affections, but Hikaru doesn't really take her seriously. Poor Primera!
Nova
When the anime was created for the second season of MKR, the director and CLAMP apparently realized that there wasn't enough story about the three invading countries to play out for 29 episodes. So two new characters were created to cause even more trouble for the Magic Knights: Nova and Debonair. Nova bears a slight physical resemblance to Hikaru (although she's inhumanely skinny) and is obsessed with her. No one but Hikaru knows she exists, as she communicates with - or rather torments - Hikaru in her dreams. Who is she, and what is her relationship with Debonair, whom she calls "mother"?
Debonair
Debonair is the ominous "big bad" lurking in the background of the second season, but she appears only in the anime. A scary-looking, unworldly presence who haunts Hikaru's dreams, Debonair-sama ("Lady Debonair") keeps trying to break thru from a nightmarish shadow world into the Cephiro's reality. She appears infrequently and generally works thru Nova to get to the Magic Knights.
Aska, Sang Yung, Chang Ang
Eagle Vision, Geo Metro, Zazu Torque
Tatra and Tarta
These are the twin princesses of the Arabian-like world of Chizeta. They also wish to become Pillar (I'm not sure if they intend to share the position or if Tarta, the more determined sister, is planning for it). They have opposing personalities: the older sister, Tatra (loose hair), is very calm and dignified at all times, and has a penchant for serving tea and being amusingly polite. Tarta (braided hair) is much more direct about her ambitions to annex Cephiro to increase the size of their tiny country and is frustrated by her sister's laidback nature when in the presence of their enemies. She is a match for Umi, while Tatra is more like Fuu. Both Tarta and Tatra have the ability to summon two guardian deities called "Djinn" (male genies, the word is Arabic for demon or spirit) whom they magically control like avatars. The djinns' names are Rahkun and Rasheen (Rashid in the English manga) and they always manage to creep out Umi.