I live in Japan. You'd think I could just find ivermectin at candy stores or whatever, but I really do not know where to begin looking for it---at least not without some prescription. The home center sells antiparasitics for pets, but the selection is very limited. I found something called piperazine. I did a bit of research.
https://applbiolchem.springeropen.com/articles/10.1186/s13765-021-00651-0#Sec12 "can act as an anticancer chemotherapeutic by stimulating the intrinsic mitochondrial signaling pathway to induce cytotoxicity and apoptosis in cancer cells."
https://peerj.com/articles/1588/ "displayed a strong suppressive effect on liver cancer cells"
I'm finding a bunch of articles on Yandex, but I am not highly scientifically-minded when it comes to so many various medical terms. If you wanna read something hilarious that came up with my search on piperazine, check this babblespam. It's so funny.
https://gujaratmitra.in/S6C0feUok-male/piperazine-erectile-dysfunction-M90WcK/
KEK! Reminds me of those bizarre spam email from the early 2000's.
So... erectile dysfunction? I think piperazine enhances nitric oxide, and so does L-Arginine. I take L-Arginine for health and exercise potential. Apparently it plays a part in immunity, anti-fungal, etc.
I have to say this as respectfully as possible, but this is the kind of post that is exactly why I wish people wouldn't do their own research. So much of what we learn requires context to understand. Requisite information is critical. This is why a lot of the secret societies have initiation as well as various levels of involvement through which you are taught a little more each step as you go. You can't hope to understand differential equations without high school-level introductory algebra, right? In this case, a background in organic chemistry is necessary to understand pharmacology.
Here (Wikiwand link) is a good explainer.
Piperazine isn't just one molecule. It's a class of molecules. It's a 6 membered ring with 2 nitrogens integrated at opposite ends of the ring. There are many molecules with various added atoms (called moieties) that are members of the same class because they possess this ring. They have some common properties, but vary based on the extra parts attached to the molecule.
In this case, I think you're looking for a specific on that Bayer used to market as an antiparasitic, specifically an anti-helmenthic agent. Look up helminths if you want to learn more about the specific worms called helminths that this drug is intended to treat. Again, there are lots of different piperazines and that link I left has a list of dozens of piperazine compounds, most with absolutely no anti-parasitic activity at all.
As for cancer, I'm cynical. Cancer is an extraordinarily complex topic and we read sensationalist headlines all the time claiming this thing or that thing causes cancer or treats it. Most of it is bull, and it's hard to sort that out without having some high quality randomized, placebo-controlled clinical trials with a good sample size of patients. I know on this website, people are claiming ivermectin is the next miracle drug. It may be in very specific cases. I've read case reports like that, but I've also read larger studies that failed. The higher quality evidence points to it not working. So, it's important to be careful about such claims. I wouldn't chase down piperazine in Japan hoping against hope that it'll cure some newly diagnosed tumor.
As for finding it in Japan, you'll want to find the Japanese name for it. It was invented in Japan from a Japanese soil bacterium, so without a doubt if you search for the history of it in Japanese, it should have that name in Japanese characters. Then you can ask your local pharmacy. It became a political football in Japan over COVID just like it did here, and there are reports that doctors were compounding their own during COVID, which makes me think there were restrictions put in place on its sale, but trying to search on US search engines is absolute cancer for this kind of thing. Everything's scrubbed and curated.
Give them a break anon. It is extremely hard to find real results and studies on this information unless you know where to look. Most people will go to Google and be false information about IVM being dangerous etc.