Essential Material: Resonance of Saint Graph (Patreon)

In a word, harmonization. The degree and strength of the connection between Taylor Hebert and the Heroic Spirit which she Installs. The level of synchronization between her and the Heroic Spirit. The more complete the harmony, the more she can display the power and skill of the Heroic Spirits.

There are several factors that affect this parameter. One such factor is the situation: by utilizing a Heroic Spirit that has a connection to the situation via either an event in his legend or his strong feelings (regrets, trauma), the degree of cooperation between her and the Heroic Spirit is increased. 

As an example, to utilize the Heroic Spirit, Siegfried, in a situation involving a dragon, the Heroic Spirit's true strength can shine through most completely. This is a result of Harmonization of Ego Pattern, where the mindset of the Heroic Spirit and the mindset of Taylor Hebert are in sufficient agreement regarding the situation. 

Another such factor is how deeply Taylor Hebert draws upon the Heroic Spirit. Though most scenarios only require a basic level of cooperation, such that the influence of the Heroic Spirit's ego is negligible or almost unnoticeable, if she draws upon the personality and experiences of the Heroic Spirit to help her handle not only the rigors of physical combat but also the mental stress of the situation, the ego of the Heroic Spirit becomes more pronounced. In this case, she will display personality traits and act more in line with that of the hero she has Installed.