1. Konohamaru: Despite possessing formidable skills, such as the Sexy Jutsu, Rasengan, and Shadow Clones, Konohamaru, Naruto Uzumaki's disciple, was unable to join the Fourth Ninja World War as he was only a Genin at the time. 

2. Yugao Uzuki: However, due to her limited appearances in the series and pregnancy, she did not participate in the war, and her potential was left untapped. 

3. Ibiki Morino:It remains unclear why he was overlooked and did not participate in the war.

4. Kotetsu Hagane: He also did not participate in the war, despite his abilities that could have easily overcome the White Zetsu Army and held his ground against the Reanimated Shinobi Army. 

5. Teuchi: Speculation arose among fans that Teuchi could be a powerful individual, possibly related to the legendary Kaguya Ōtsutsuki clan. This missed opportunity could have revealed his rumored legendary strength.