closedeyesoflove

Subconciousness [This is all mun speculation. It is unknown in canon that she can do this, but these are my ideas regarding what her abilities incorporate.]

Abilities:

Ever had that moment where you put something down and then it disappeared? Only to find it located in another area? That would be Koishi at work; grabbing something of her interest and then leaving it when she was done.

Since Koishi is largely driven by her subconscious desires, physical intimacy such as hugs, kisses, and cuddling come naturally to her. She sees no real problem or romantic subtext to such things, simply doing them as friendly gestures.

If Koishi ever really wants to convince someone to do something or agree with her, her tone and body language subconsciously shift to project subliminal messaging to attempt to will that person over to her way of thinking.

In addition to the above, from Chirei-De; Koishi can possibly channel her subconcious behavior; either by touch or by using body language.

Koishi can also ‘spirit away’ people in a sense that they will have a sensation of them going somewhere in a trance. It can be broken by an outside influence either by shouting or by interference. After being broken by this trance, one would feel as if they have no recollection of why they were there or going in the first place.
[Ever had that experience where you go somewhere and completely forgot why you were there or going to go? This is pretty much that experience.]

That also said, Koishi can manage to make people speak Freudian Slips a lot more when they’re around her. Or she may misinterpret things to make it sound like a Freudian Slip.

Koishi generates a “Someone else’s Problem Field” effect; She is generally unnoticeable unless she is seen in someone’s direct line of sight. When someone finally notices her, then she becomes noticed within the immediate area.

Even if one can see her with their eyes, it would feel as if she did not exist, like a living mirage.
To the eyes of children she is the equivalent of an imaginary friend. 
Those with ties to the supernatural can FEEL as if she’s there, sense of her presence or the feeling of ‘one being watched’.

Empath related powers; given how she deals with subconscious, she will be able to see through ‘masks’ people have made themselves and see their true emotions.
 Essentially a tsundere’s worse nightmare as she’ll be able to tell their true feelings.
 Also very bad to be around with people who have unresolved trauma in their lives for she might stir up some memories of such events.

http://en.touhouwiki.net/wiki/Koishi_Komeiji
Touhou Wiki Link

http://en.touhouwiki.net/wiki/Symposium_of_Post-mysticism/Koishi_Komeiji
Symposium of Post Mysticism summary

Summary:
Koishi is a species of youkai known as a satori; youkai capable of reading people’s minds through the Third Eye placed above their hearts. However, because of this ability she and her sister have become hated and despised, and eventually they self exiled into the Forgotten Hell.

Even in Hell though they were despised for their nature. Koishi, no longer able to deal with the hatred, closed her Third Eye to prevent herself from reading minds. This backfires on her; Koishi has become carefree and aimless, hardly attached to anything. She’s gained a completely different ability instead as well, manipulation of subconsciousness.

After the events of Subterranean Animism, Koishi returns home and learns of what happened; Satori losing to a powerful human ousider and Okuu gaining the power of Yatagarasu through Gods. She decides to visit the Moriya Shrine, who’s gods granted Okuu this power and encounters the protagonists instead. Challenging them to a fight and losing to them, she came to a realization; if there are just as powerful and interesting people on the surface world, perhaps she wouldn’t have minded keeping her Eye opened.