And the worse part is that Reimu is entirely right. And she even forgot the part about Kasen constantly nagging her.

Kasen is an egotistical know-it-all that treats Reimu like shit. Reimu has every right possible to kick her ass as explained above. Also the nagging she is capable of producing can kill children.

If Kasen wins she will nag her more

Kasen is not that bad. She's not perfect and has her own "egoistical" goals, but she also did some good things. And she isn't any more annoying than Shiki is.

A list of reasons why Reimu holding a grudge against Kasen:

1. Forced Reimu undergo hermit (zoo) training against her will? Check

2. Poisoned by a raijuu which happened to be Kasen's pet? Check

3. Embarrassed Reimu in front of public for falsely claiming there was a dragon inside the wet stone? Check

I wonder if this also includes the time where Kasen took care of the Hakurei Shrine during daytime and she inadvertently (actually purposely) attracted many youkai to the shrine. As a result, rumors started to spread about youkai roamed and enjoyed freely around the shrine, which caused uneasiness and lost of faith to the Hakurei Shrine by the human worshipers.

Furthermore, this also caused human visitors lost faith in Reimu's fortune telling and ultimately, ruined her business to dust. [Chapter 23]

the funny thing is , kasen would get in trouble if she would fight reimu at full power
she says so in the story mode when facing her.
Kasen too OP confirment.
I wonder how reimu reacts to kasen not being human, sadly new chapters of WaHH have been rare

I feel being a bad teacher, being a know-it-all, etc., serves a purpose. Not only that she doesn't truly know what makes Reimu tick, but that she doesn't know what it means to be truly wise hermit. It makes sense considering her secret and all her recurring doubts and insecurities. She has all the pretense of a hermit and some of the knowledge but not much of the wisdom. She's playing hermit, imitating what they do, in short.

Tio124 said:

the funny thing is , kasen would get in trouble if she would fight reimu at full power
she says so in the story mode when facing her.
Kasen too OP confirment.
I wonder how reimu reacts to kasen not being human, sadly new chapters of WaHH have been rare

I don't think we're to that point. Though more doubts by Reimu and Marisa have come up recently. Not yet that she's really an oni, but about her hermitude.

ULiL even seems to take place in current continuity, taking place after chapter 26, and includes her without giving away her secret. Something ZUN has been reluctant to do until now.

[KN] said:

Kasen is not that bad. She's not perfect and has her own "egoistical" goals, but she also did some good things. And she isn't any more annoying than Shiki is.

Thing is, Shiki rarely shows up as long as you stay away from Muenzuka. Heck, when is the last time she ever showed up in any meaningful form in any of the canon games or manga after PoFV? Kasen goes to Reimu uninvited to nag her regularly. You can avoid Shiki until you die, but once Kasen decides to get up all in your business, you're stuck with her.

Oh, and let's not forget the Hopeless Masquerade tie-in chapter of WaHH, where Kasen started rooting for Reimu outloud in order to distract her, so Kasen could collect on the bet she placed on Byakuren winning! She causes far more problems for Reimu than she helps solve. Kasen totally has an ass-whupping coming to her!

Tio124 said:

the funny thing is , kasen would get in trouble if she would fight reimu at full power
she says so in the story mode when facing her.
Kasen too OP confirment.
I wonder how reimu reacts to kasen not being human, sadly new chapters of WaHH have been rare

Way would she get in trouble , is not like she will kill her , so i don't get way she would get in trouble.

razer666L said:

A list of reasons why Reimu holding a grudge against Kasen:

1. Forced Reimu undergo hermit (zoo) training against her will? Check

2. Poisoned by a raijuu which happened to be Kasen's pet? Check

3. Embarrassed Reimu in front of public for falsely claiming there was a dragon inside the wet stone? Check

I wonder if this also includes the time where Kasen took care of the Hakurei Shrine during daytime and she inadvertently (actually purposely) attracted many youkai to the shrine. As a result, rumors started to spread about youkai roamed and enjoyed freely around the shrine, which caused uneasiness and lost of faith to the Hakurei Shrine by the human worshipers.

Furthermore, this also caused human visitors lost faith in Reimu's fortune telling and ultimately, ruined her business to dust. [Chapter 23]

iirc, most of those were basically Reimu's own fault.

Reimu's sloth is characterized to be, ultimately, a bad thing. Forcing Reimu and failing to rehabilitate her into an actual hard working human being isn't exactly deplorable behavior. Especially since the reason the training failed was because Reimu's Reimu.

The raijuu poisoning was Marisa and Reimu's fault since they had captured it and was actively trying to profit off of it and this was karma's way of biting them in the ass. Neither was the raijuu really Kasen's responsibility either; she cared for it when it was running wild, before that it was just a regular supernatural animal running around Gensokyo. I also don't think they are even aware that Kasen knows this particular raijuu.

I don't remember Kasen ever claiming that a dragon existed in the stone, only that books say so. Then Marisa and Reimu ran off and jumped to conclusions before listening to the rest of what she had to say. Then Kasen explained that it was actually a dragonfish stone, then Marisa went ahead and chipped it apart making it lose all of its value.

Sure Reimu could blame Kasen, but most of why Reimu's get-rich-schemes all fall apart is because she's being greedy and her avarice overrides all her common sense thus leading to public embarrassment. Kasen, more often than not, tries to help Reimu. Reimu, being the completely reasonable and rational individual she is with regards to money, decides to do whatever seems most profitable in the short term and forges ahead with whatever scheme she first thinks up without foraging for information or being the slightest bit prudent.