Self: The number that represents the integrity of your soul. Defined by your own sense of identity, your own ego, and the recognition of others, as a warrior fueled by the power of your own spiritual energy, the Self could be called your lifeline, your most basic and most precious characteristic, as your very spirit depends on it. If your Self is in a low value, hits zero, or hits negative values, many bad things may occur, although there may be the possibility of getting benefits out of it, depending on the situation.
Self Loss: There exist many events in Titanomachy that can reduce your Self value. Ranging from a direct interference in your soul, as happened at the end of the Prologue, to attacks on your mind, to certain kinds of insanity, to the loss of someone precious to you. Enhanced Humans, beings that have achieved a measure of control over their own soul, can control the loss of their Self somewhat, and are able to voluntarily reduce it, converting it into an enhancement to their own body, which has become deeply connected to the soul. Half of the Self voluntarily lost can be converted in stat points for a single turn.
As an example, Taichi lost 10 Self, and converted them into 5 points of STR for this one turn, which he used to hit the Faceless One even harder.
The current maximum of stat points obtainable via this method is 6.
10 self can be sacrificed once per day to obtain 40 HP or SP.
Self Gain: Self can be recovered by certain events, as well as by augmenting the Relationships of your character, both in depth and in number. Also, like with SAN in Onigokko, you can attempt to transfer some of your own Self (for a maximum initial value of 5) to someone else, although this must be roleplayed, and in the case of the NPC, whether he or she will accept the Self points is up to how you do it, and the GMs decision. Each rank in a Relationship with someone else allows you to transfer an additional 2 Self to him or her (25 becoming the maximum at Relationship 10).
Possession: One of the many things that can happen when having low Self. Once Self is lower than 30, possession by one of the many spirits inhabiting this world becomes possible. Possession, however, only happens under certain circumstances, and the personality of the vessel also determines what kinds of spirits can possess them. There are many unknown details of how possession works, but once one’s Self reaches 0 or below, chances of Possession become extremely high.
Mutations: As one’s Self approaches zero, effects can be noticed in the personality and the mindset, but none of them transcend to the realm of the physical… at least until one reaches 0 Self and beyond. Once that happens, and every ten points of negative self afterwards, there is a chance of undergoing a random Mutation. Mutations can vary from minor to major, and they can be a blessing in disguise, giving the afflicted increased options and power, at the cost of higher instability and easier loss of Self. The effects of the Mutations can be really varied, and as one mutates more and more, pre-existing mutations may become harsher in their effects. Each Mutation has its own particularities, and they may be affected by the background of the afflicted, even by their nationality, or their power, etc.
For example, Japanese are more prone to get Youkai-based Mutations.
The Lost: When one reaches zero Self, control of oneself is Lost, and one becomes an empty creature guided by mere instinct that will consider everything nearby a threat, and thus will attack on pure instinct. The target possesses all the skills and abilities it possessed before becoming Lost, but its Spiritual Rank is halved, then multiplied by ten, and the result is distributed between their stats, acquiring more raw power in exchange for losing any social function and capability of interaction in a non-hostile manner. Those in the Lost status will automatically lose ten Self on the first turn, then lose two Self per turn, going into the negatives, and only being able to be pulled back into sanity by having their Self brought up back into positive numbers. However, upon returning from the Lost status, their maximum Self capacity is reduced by twenty. As the maximum quantity of Self an Enhanced Human can reach is 150, those are bad news.
Because once one completely loses all capacity to have Self, they become permanently Lost and cannot be brought back except via extremely special or unique methods (such as one of the uses of a Philosopher’s Stone). These miserable creatures are called the Lost Ones, or merely the Lost, and are naught but wandering, mindless robots of flesh that wander the world killing everything they come across, echoing what they once were until they finally meet their end. In sum, they have completely ceased being human, and all they can wait for is for the release of death. They might undergo extreme mutation based on the Spiritual Power, which will often go out of control, and they may quickly become a danger much more fearsome than any Monster if not taken care of fast enough.
Pray that the day one of you reaches this state may never come to pass.