Not a great thing but I think it would be good for Ikki to have one of those regarding the use of Cosmos and sensing it.
First let me give a brief explanation of what the Cosmos is:
Basically the "Cosmos" is an inner spiritual essence that resides in every living being and which origin goes back to the very Big Bang. The concept of the "Cosmo" advocates that each atom within a human body resembles a small solar system, and since the human body consists of billions of atoms, the totality forms a "small Cosmo" or a "small Universe". Also since each person is unique in many traits, so are their atoms and, by extension, so is their Cosmo signature. For most living beings the Cosmos plays a minor and unconscious role in their lives, only manifesting at life threatening situations, Saints like Ikki, however, are trained to control this Cosmos at their will and make use of it to its fullest capacity.
For a less technical explanation you can somehow equal it to other concepts of inner spiritual energy like the Ki but more ample and less restricted.
Being trained since young to use the Cosmos, Ikki is naturally inclined to expand his Cosmos and try to "feel" other people. And that's where the permissions enter in action, if you would please I would like you to answer this few questions regarding your characters. Also, to safe time this is only limited to living beings, what we understand as living beings for this is "things that live and have energy/soul within them". In other words, androids and the like are excluded from having a Cosmos, but undead people with soul will have it.
Can Ikki feel your character's Cosmos? It is possible to "erase" or "hide" one's Cosmos to the point of it being very difficult to sense it. Though it's not really the same thing we shall go by the concept that if a character can hide its Ki, Chi, Force energy or whatever it's called in their canon that spiritual energy within them, Ikki won't be able to sense it. If possible detail too how much of it is hidden or if there are instances in which it won't be hidden (like in the middle of a fight).
How much can Ikki feel out of your character's Cosmos? Though it's not mind-reading, the Cosmos often mirrors the general nature of a person. Someone full of evil intentions will have a remarkably evil Cosmos, someone innocent and kind will, however, have a pure and soft Cosmos. Emotions are also often reflected in the Cosmos, the more intense they are the more they will reflect on the Cosmos making it possible to sense when someone's angry, scared, worried or happy. However all that Ikki will be able to get is a general view of their feelings and if none of those mentioned is at play he won't feel anything about the character's emotions.
Can Ikki's Cosmos affect your character? This is mostly/only to those characters who can also sense the spiritual energy of others. Thought Ikki can't control a character with his Cosmos it's possible that a character will be affected somehow if Ikki were to make his Cosmos burst and burn at its highest potential, say by being pushed down or even immobilized by the strength of it momentarily or simply feel the pressure of his Cosmos in the atmosphere growing up.
I think that's all, if anyone has any questions contact me through AIM (neurofirstslave) or ask in the comments.