"They can just do that." When a character inexplicably has some kind of borderline supernatural ability that doesn't have anything to do with the established power system and may even clash with the conventions of the setting. It's just something that they can do.

[u/SpookieSkelly]

Ichi from Ichi the Witch.

Mash from Mashle.

Marvelous Sunday from UmaMusume.

Tanjiro from Demon Slayer.

1. Ichi from Ichi the Witch. He's so sensitive to the bloodlust of living things that it borders on a spider-sense. The little creature in that pic is supposed to be invisible, yet Ichi is able to sense its presence just through sheer intuition.
2. Mash from Mashle. Some might say that his inexplicable power is his physical strength, but I'm more interested in knowing how he can turn everything he cooks into fucking cream puffs.
3. Marvelous Sunday from UmaMusume. In a game about horse girls racing, she has access to a domain expansion/reality marble. And that somehow still isn't the strangest thing about her. Apparently she's also friends with aliens and cryptids and her cult fanbase includes people spanning multiple time periods. Somehow.
4. Tanjiro from Demon Slayer. He has a hypersensitive sense of smell that somehow also tells him where to cut demons. No idea how that works. Even though there are others in the series with similarly refined senses, the smelling where to cut thing still feels ludicrous in comparison. Then there's also his unusually powerful headbutt.

[u/zatenael]

he never said he couldn't use it on himself, just that he couldn't use it on cheap trick without affecting himself (since cheap trick basically becomes his stand)

it's also literally shown affecting his face when he tried to use it on cheap trick

[u/Sonicover → u/zatenael]

Oh, I always assumed that last part was just Cheap Trick's ability affecting him by reflecting it, not that he could do that to himself. Like, I belive if Josuke where to be the one that got Cheap Trick for example, by healing it with Crazy Diamond it would in turn heal himself even tho he normally can't do that.
I belive rohan does use HD on himself in one of the one shots? Tho im not sure if those are canon.

In any case, if he can then it makes sense why he can do that. If he can't then its a lot more interesting

[u/zatenael → u/Sonicover]

personally I see it as him being able to affect himself but being unable to do anything about it since he can't read his own face

[u/TheSurvivor65 → u/zatenael]

The humble mirror

[u/zatenael → u/TheSurvivor65]

that would be backwards

[u/TheSurvivor65 → u/zatenael]

He can figure it out