Board Thread:General Discussion/@comment-24809896-20140621004139/@comment-8986886-20140819111630

I don't think Yhwach is afraid of any Bankai, known or unknown, since Yamamoto wasn't on the list, and his Bankai was without doubt the most powerful. Yhwach made the list before the invasion, so he couldn't be certain that he would be able to steal Yama's Bankai, yet he wasn't considered a threat. After Yama's death Unohana would (in theory) have been the Shinigami with the most powerful Bankai, but Shunsui didn't hesitate to sacrifice her just to break down Kenpachi Zaraki's self-imposed power limiter.

That says something about the three confirmed "Notable Threats" on Yhwach's list. Ichigo, Aizen, and Kenpachi, all have ridiculous potential way beyond that of the average Shinigami captain. Just taking powers into consideration I can't see any other captain, current or former, qualifying for the list.

Kyoraku and Ukitake are the most senior, now living, captains and should have powerful Bankai, but they are hardly a match for Zanka no Tachi, and probably not for Minazuki either. Tessai and Hachigen are Kido masters and know forbidden spells, but they're pretty close in strength so either both of them are on the list, or neither one. Yoruichi has Shunko, which is a powerful technique no doubt, but so does Sui-Feng, and I don't see how her speed, or assassination skills, would elevate her to Ichigo/Aizen/Kenpachi level. That leaves intelligence and inventiveness, which Kisuke and Mayuri have plenty of, and I'd rank them pretty close since Kisuke is smarter, but Mayuri has the whole S.R.D.I. under his command.

To sum things up, these eight Shinigami might qualify for the list, however they're not unique in any way: Experience - Kyoraku and Ukitake, Kido - Tessai and Hachigen, Shunko - Yoruichi and Sui-Feng, Intelligence - Kisuke and Mayuri.

Some other prospects are the Royal Guard members, since Yhwach can't possibly know anything about their current powers, however, he wouldn't even know their names or faces. The Soul King himself, for obvious reasons, Uryu, who has been praised by Yhwach for his potential, and Orihime; though Yhwach didn't know her name when he mentioned her to Yamamoto, so I doubt she's on the list. Finally, Tsukishima has a unique power, and might pose a threat to Yhwach.