For kanji I initially have trouble remembering, I try to focus very specifically on the mnemonics, not just in terms of a story, but a feeling. Many of the mnemonics already encourage you to do this–to picture yourself in some kind of shocking scene. Try to really do that; if they don’t include the suggestion already, find a way to get into the scene yourself.
If you can make a connection between the kanji and an idea–any idea–you’ll have a much easier time remembering it.
Also, it’ll only get easier. I know that sounds crazy, as it’ll only get worse in terms of workload, but if this is your very first exposure to Japanese, starting to understand the rules and patterns of the language (and of kanji and readings themselves) will make acquisition of new items go smoother and smoother. So on that note, if you aren’t already also diving into foundational grammar and vocab outside of Wanikani, I’d definitely recommend doing so. It’s just one specific piece of Japanese-learning, and I honestly think without the others you’re making it harder on yourself than you need to. The only thing more difficult than remembering vocabulary and pictographs from a foreign language is remembering them with no context to put them into.
Since Wanikani also isn’t a site structured around the complexity of its vocab, but rather the complexity of its kanji, you’re not necessarily getting those easy little starter words like you would with a general language course (in the way you can teach any kid colors, animals, etc. in English and have them stick even without surrounding grammar). So again, having the more general context is really going to help. Just memorizing a random grab-bag of vocabulary in a foreign language is really going to be rough.
(I don’t actually know if it’s the case that you don’t have a grammar foundation yet; was just going off your first post wondering if the ability to learn a new language had passed. If you have that already, I’d just focus on really visceral mnemonics that involve the radicals.)