@additionalramen Good news — I just made exactly this! It is called WaniKani Review Analytics and it adds a panel to your dashboard showing daily/weekly accuracy trends, SRS breakdown, and item type analysis with interactive charts.
It uses Chart.js and fetches data via WKOF (WaniKani Open Framework).
Install: WaniKani Review Analytics
Forum thread with details: [Userscript] WaniKani Review Analytics — Track your accuracy over time with charts
My GitHub: bimapopo345 (Bima Prawang Saputra) · GitHub
Let me know what you think or if there is anything specific you would like added!