Yeah, the one I had the most trouble with at first was Jiraiya. I always spelled it Juraiya lols. Afterward, it was mangekyou, which I often spelled mangenkyo. After that, it was Tsukuyomi, which I often spelled tsukiyomi, though those aren't characters. I had a lot of trouble with the seven swordsmen's names too. Kushimaru Kuriarare, Fuguki Suikazan, Jinin Akebino, etc. I don't have an issue spelling Ootsutsuki per se, just typing it lols. I also had issues spelling Katsuyu, which I spelled Katsuya for a long time and Gamakichi, which I spelled Gamakishi.