Hau is a nice, cheerful boy. He gives you presents. When defeated in battle, he is gracious and tells you that he had fun. Nothing about Hau seems competitive, which might explain why Pokemon players keep theorising that he isn't your real rival in Sun and Moon at all.
Image source: Mixeli
Historically, Pokemon fans associate the word "rival" with "arsehole". In Red and Blue, it was tradition to name your rival the worst curses you could think of, and these games cemented what fans expect from a Pokemon rival. Hau embodies none of those negative traits: Really, he's your buddy in Sun and Moon.
The effect is that Pokemon players keep insisting that Hau is not your rival. In particular, one theory points out a number of odd choices the developer, Game Freak, made for Hau. When you pick a starter at the beginning of the game, Hau picks the creature weak to yours. Historically, rivals go right for the monster that would be strong against your starter. Hau also carries a Pikachu, a Pokemon that players associate with the "main" characters. Finally, you always seem to be one step ahead of Hau, clearing trials and battles before he does -- fans still have memories of the Red and Blue rival defeating gyms first. Taken together, some fans now have the conspiracy theory that the player is the rival (ignoring, yes, that a rivalry requires two people).
Since release, players are constantly questioning Hau's status as a rival:
Hau has the starter weak to yours, a pikachu and beats the trials after you already clear them. It's you. You're the rival.
— Chorocojo (@Chorocojo) November 24, 2016
Hau is not a rival he is a friend
— Dylan (@squidgerydee) November 27, 2016
Hau doesn't even feel like a rival like he's not competitive at all he's just HEY BUDDY HERES SOME USEFUL ITEMS UR THE BEST UR AWESOME
— PLAPPY PLANKSGIVING (@plekdraws) November 24, 2016
Hau is pretty much how I picture the main character of every Pokemon game which makes me think WE'RE the rival in this one
— ThirtyHelens (@30_Helens) November 23, 2016
My rival isn't a true rival. He just wants to hang out. Good for you, Hau. I wanna hang out too. Let's ditch this quest.
— Jessie Radgowski (@JayRadHype) November 19, 2016
hau's pokemon doesn't have type advantage...? he isn't my rival..?
— ☆°~ tyler ~°☆ (@todorcki) November 19, 2016
Also Hau's Pokemon is weak to mine?
Are we going to have another rival?
— ChristmasAlbertree? (@GuardianYoshi) November 18, 2016
I love how Hau isn't the actual rival, but it's YOU who's the rival, your starter is strong against his and everything.
— bunloaf (@sleepylunar) November 27, 2016
Wait, it just hit me. Hau isn't the rival...we are. Holy shit...
— Dork (@Dorkshadow) November 28, 2016
OMG! I'm the rival, Hau isn't the rival I am! #Pokemon
— Lore_Retro (@Lore_Retro) November 28, 2016
@WarioWare3DS no, hau isn't the rival
— PKMN Trainer Ryan (@GeneralistGamer) November 28, 2016
Here's where things get interesting. While Hau may not fulfil our expectations of a rival, there is another character in Sun and Moon who fits the bill rather nicely: Gladion, the Team Skull minion. From the outset, Gladion's very appearance looks menacing, especially when placed next to Hau's wide, doofy grin. Gladion is also terse and combative, immediately demanding skirmishes for no purpose other than to flaunt strength:
Image source: Mixeli
When Gladion loses, he seems devastated:
Image source: Mixeli
It appears that Gladion captures the spirit of rivalry we've come to expect from Pokemon games, but hardcore fans are also pointing to a more compelling piece of evidence. Hackers and data miners claim that the in-game files don't refer to Hau as the rival at all:
@xpatriciah bgm_nj_vs_rival.dspadpcm.bcstm is Gladion's theme iirc
— Saint Nikki ❄️ (@NWPlayer123) November 26, 2016
While I can't dive into the files to verify this, we can all hear a difference in the songs. Hau's battle theme is happy-go-lucky:
Gladion's theme, on the other hand, sounds epic, like a serious showdown -- which is what people expect out of rival battles.
Maybe the song file stuff is bullshit, or an oversight on Game Freak's part. Whatever the case, one thing is clear: Fans are holding on to an old rivalry framework, and it's influencing how everyone interprets poor Hau. Sun and Moon aren't the first games to change the paradigm -- X and Y gave players multiple rival friends to battle throughout the story, all of which weren't outright adversarial, so really, this is nothing new.
Still, it's pretty fun to think that maybe the rival isn't who we think it is.
Theory via suchomochlus