Well , I did said he travel with his childhood friend who seem to have a crush on him. She act like his manager and often straighten him up.
Also , We could have rival based on bully from classic Japanese anime like Doreamon Or perman .
A boy who travel with 2 lackey and often tries to cause problem for the protagonist but slowly become good friend with him. He also attracted to Serena and envy Ash for her.
Or A Absent-minded girl with sharp tong like Marley who doesn't have any sense of Direction so her cousin accompany her. Despite her absent-mind , She's a capable battler who nearly defeated Ash in Double Battle. Her cousin have a habit of hitting her with paper-fan everytime she say something stupid. Her cousin happen to be a girl as well.
Or A rich girl who travel with her perfect Butler with inhuman ability.
There just so many ideas .
Okay I get Why Ash can't travel alone !!!
But Can't Writer give him rivals who also travel with a group ???
Is there any need for Ash to be the Onlyyyyyyyy Challenger in the series who travel with group ??
May Be Writer can gave his rival more in-death characteristic if they also has a traveling companion .
How about a Playboy rival who travel with his childhood friend and self-proclaim fiance !!!
He often flirt with Serena Or any other girl and get beat up by his traveling companion for it .
Clemont Or any other boy can't stand him because he not only attract most girl toward him , he also taunt other boys for being unpopular with girls.
Ash is only boy who can stand him because he's too dense to understand his insult !!
While he envy Ash ever since Ash stole the attention from other girls by defecting team Rocket and being the Hero from ''Garchamp incident'' .
He can stand the fact That Someone like Ash can be popular with girls who think ''Romance'' as some sort of Pokemon and who's mother still pick dress for him .
He descried Ash as a Worst Womanizer then him because Ash doesn't know he is a Womanizer .
You're right that there's an awful lack of female challengers. But the only real way to do that would be to make Ash's main rival a girl, because showing dual gym battles every time? Ugh boring. Hopefully he'll have a female rival this time though. I mean why not, right? Since they're obviously balancing the gender ratio of the main group, then it seems logical that they'd get more gender equality into the series.
When the last time Pokemon had a powerful female challenger around Ash's age ??? I called Ash's profession ''Challenger'' Because if I said Trainer then you would use Zoey , Maylane ,Duplica, Shauna, Dawn , May etc as example .
I talking about a girl who also participate in Gym battle and trying to win Pokemon League .
Honestly , I can't remember anyone after Maecy from Jotho league .
Although there were some challenger But they ether a newbie trainer Or a gag rival like Bianca & Cassy .
Its ironic that this anime didn't had a single powerful female Challenger around Ash's age for 15 years.
When XY started , I was sure there going to be a powerful female challenger but now I doubt if Ash going to have any rival at all .
Writer could create another Giselle who even more stubborn , Meaner, arrogant , Prideful , strong , Prettier & antagonistic then Giselle as Ash's rival.
Writer already recycle that ''Gliger-man'' from Jotho 2 time So what is the problem in recycling Giselle.
Or Then could create a female rival with Ash's Snivy's Personality . A girl who has reddish brown hair with long side Ponytail.