@Chizan
There was a chapter (I forgot the number, but it was the one where the Head Priest's daughter was introduced) where her friends (one of whom is Hosshi's (the nerd's) sister) passed by Komainus. One girl saw them as dogs, Hosshi's sister saw them as children. As a note of reminder, though, Hosshi's sister is quite infatuated with the concept of Ayakashi, even listening to the Ayakashi radio at nights.
Further things to note that has been outlined throughout:
- For obvious reasons, the Head Priest and his daughter are fully able to interact with the Ayakashi. Additional characters that get thrown into this category of humans include the Old Man (who draws homeless Ayakashi and is presumed to be 'God') and the two priests that were trying to do service on a broken doll's house (both seen in ch 46). I suppose the Shikigami teen girl exorcist falls into this category too, though Ishiyama (the exorcist with the Ayakashi-sword Kurogane) falls more onto the 'possessed/companions with Ayakashi' category (both seen in ch 90)
- Chika's friend, despite completely ditzy and a complete side character seems to have no problems seeing Kurona's Ayakashi form, though she has to be explicitly shown it (I forgot which chapter this was). In comparison, even children slightly older (chapter 107) seem to not notice Kurona's Ayakashi form and has presumably seen her as a girl despite the ears and tail. Older characters may see discrepancies in an Ayakashi's human form disguise (especially if said discrepancy is so outragous to the point where no typical "human" should ever be like such), but still ultimately consider the Ayakashi 'human'... just a very, very weird one.
- Kokkori has noted several times (ch 55, ch 35) that children eventually grow older and "forget" the Ayakashi. Ch 55 implies that this is even true for the children these spirits have possessed at one point. Granted, though, certain children (like Chika) are far more sensitive to Ayakashi than others. So far, the only other child character that has a spirit bond relationship would be a minor character who plays card games (Makoto from ch 63)
Basically, it boils down to how, unless the Ayakashi is purposely intending to show off their form, or unless their powers grow out of control, only children (who are open to imagination and not jaded by the reality of life) and people with spiritual powers can see their Ayakashi form. It's still highly suggested to keep ears and tail in if only because it seems that the people with spiritual powers do not bother with boundaries in this world, and it is too much of a risk anyways if someone with a stronger sixth sense wants to seal them all.