Someone pointed out that (i forgot which page) that Arle is friendless, and everyone outside of Yon and Shin Madou had a major beef with her and hung with her out of habit. Can someone please tell me why? Come to think of it, until Fever era, no one from the Compile era had friendship with anyone else. Everyone pretty much kept to themselves and did their own thing. The anniversary games are the only ones where characters other than the "A" Trio actually interacted with anyone else. I often felt Arle post fever was a weak character who just got annoyed with people, but now that i think about it... *everyone* in Compile is like that.
I blame a lot of that on Compile's writing often not being very consistent, for instance, you can't really apply any depth from other sources to anyone in the first three Puyo games, since everyone in those was a one-dimensional joke character, due to the excuse plot nature of their narratives. Rulue just wanting to be left alone might apply to her in some games, but then you get things like SUN, where she's the one who's egging Schezo into a confrontation.
That's a general thing, a lot of characters act quite different depending on the game, Schezo is somewhat more amiable in something like Waku Waku, but then you have something like the Saturn game, which plays up his more antagonistic qualities (which I think suits him more, but I digress). Heck, Schezo becoming less of a monster after Madou 2 isn't even the result of any stated or shown development, he's just a different character later on.
Plus, the games really weren't commited to many consistent relationships, Arle/Rulue was one of the closest things to a friendship that you could get and did come to play in a number of games, but then there's other games where you really wouldn't be able to tell that those
two are able to communicate without fighting, like again, the first three Puyo games.
Lagnus is one of the ones that could have served as a friend for Arle, but Arle never even recognizes him between games, apart from Chronicle, which was made by SEGA, so really, there is no known relationship between them in the games at all, since almost every encounter acts like it's their first one.
Everyone else just doesn't interact much with each other, likely a result of many characters simply never getting enough spotlight. The SEGA games have their own issues of focusing too much on the same few dynamics or the Arle/Amitie/Ringo/Satan/Ecolo group, but they try a lot more, I mean Quest can give us character combinations like Sig/Jan or Strange Klug/Kikimora or back in 15th we got Zoh Daimaoh/Akuma or Arle/Oshare Bones.
Then again, this is coming from the perspective of someone who thinks that Compile's writing was every bit, if not more flawed then SEGA's, supplementary materials only do so much to me, especially since much of it never even comes to play in the games, so stuff like Shin Madou only improves things so much for me.