Nidai Kitetsu is one of the 21 Great Grade swords. Like all Kitetsu swords, this one is a “Cursed Sword/Blade”. As one of the 21 Great Grade swords, Nidai Kitetsu is among the finest blades in the world, being the second strongest of the Kitetsu swords with extraordinary sharpness and strength, on par with legendary swords Wado Ichimonji, Shusui, Enma, and Ame no Habakiri.
When the Nidai Kitetsu was revealed, most people assumed Zoro would get this sword, replacing the Sandai Kitetsu with it. However, with the Strawhats now leaving Wano, this doesn’t seem to have happened.
Now Oda could reveal that Hitetsu gave it to Zoro off-screen next chapter, much like how Niji gave Sanji the raid suit off-screen. But assuming this doesn’t happen, I believe that this sword will be used by Momonosuke, alongside Ame No Habikiri.
The Nidai Kitetsu was made by the Kozuki family, so if anybody has any claim to it, it would be Momonosuke. Furthermore, Momo stated he wanted to surpass Oden. As we know, Oden used a two sword style, a two sword style he then taught the Scabbards.
I think its very likely that Momonosuke will learn two sword style from the Scabbards, using the Nidai Kitetsu as his second sword.
Momo getting the Kitetsu also makes sense because we have seen how he looks up to Zoro, who has the Sandai Kitetsu. So I think it would make sense if Momo wanted to use a cursed sword like Zoro does.
Theory by Kenny_Brahms (https://www.reddit.com/user/Kenny_Brahms)