Where can I find the copyright owner of the anime? Do I really need it for fan products? I’m recently thinking about creating enamel pins so I can make some money and save up, but since I want to design the pin with anime’s such as Toilet Bound Hanako kun and Cardcaptor Sakura, I am afraid that I will get sued for making fan products.
Do we really need the copyright owner to approve if it is just a fan product?
For legal questions such as these, it is always good to contact a copyright lawyer in your country. Laws regarding fair use, copyrights and the likes differ per country, and a copyright lawyer should be more than capable of answering your questions. And this answer should not be seen as legal advice.
Beyond that, yes, you'd likely need a license. And should contact the original IP holder (or their legal departments) to obtain it see also Who do I contact regarding rights licenses of specific manga/anime characters?
To quote sharur's answer on Law.SE addressing the creation of fan-made merchandise of the game Overwatch.

... This is exactly the situation that IP law (e.g. copyright and trademark) was created to address. Blizzard created the game and so they have rights to control and benefit from derivatives there of. There are some exceptions, but prints, buttons, and keychains are not likely to meet the requirements for those.

Additionally, you can also take a look at Printing copyrighted logos on t-shirts/jackets/apparel without permission: in which situations is it legal? which covers another angle on a similar idea.