Board Thread:Questions and Answers/@comment-2197197-20160911070805/@comment-1210805-20160913041836

Loki 71 wrote: True but lets not forget, Yachiru; name non-withstanding, had been seen by others for years and years on end. Plus the only reason nobody saw her when Zaraki's Bankai activated was because they were all too distracted by the enemy, But this explanation kinda drives the point of the matter home. Plus lets not forget names of a zanpakto tend to change when Shikai transitions into Bankai; again the name is non-withstanding, since we don't know either her real name nor the name of Kenpachi's Bankai. As I explained above, a manifested Zanpakuto can be seen by anyone. That is the key difference between manifesting it, and simply seeing it as many have done before (ie, Ichigo and Zangetsu during the latter's battle with Kenpachi).

Yachiru was shown to be invisible to everyone else in the battle with Gerard. There were many panels where Kenpachi was alone in that fight, with Yachiru only appearing when she had something to say. A writer would only do this if they wanted to demonstrate that she can only be seen and heard by a particular character, in this case Kenpachi.

Names are irrelevant in this case, as you yourself pointed out.

Khaotic Twist wrote: Yoruichi and Renji were able to see Zangetsu because of the Tenshintai. No one else saw Zabimaru but Renji. Cang didn't see Hyourinmaru. Lille didn't see Katen Kyoukotsu. Kyoukotso had Nanao's Zanpakutou, that's why she could see it at the time. Any evidence of that claim. Yoruichi explained that the Tenshintai forced the Zanpakuto to manifest, but no one claimed any other difference between that method and the standard method of manifestation. Indeed, Renji expressed no surprise at seeing Zangetsu when Ichigo was training, once again suggesting that the manifested spirits are always visible to others.

Renji made a point of showing he could manifest Zabimaru, it would have been a pointless display if Ichigo couldn't also see it.

The quincy didn't steal the spirits (otherwise the Shinigami would have also lost their Shikai), so Cang Du means nothing.

Lille didn't see Katen Kyoukotsu because she wasn't actually manifested. She appeared to Shunsui like Zangetsu did to Ichigo in the battle against Kenpachi. Your whole Nanao/Kyoukotso theory relies on the idea that a Zanpakutou can take something physical without being physical itself, and then appear physical only to someone who has a connection to that particular item, which is just inventing far more rules than simply looking at the evidence presented in the story.