When using the knowledge of Summoning Arts granted by "miracles" to summon a Familiar, no conditions were needed because the "miracle" served as a link. As long as the summoning ritual could be successfully performed, an Absolute Contract could be directly formed with the summoned target, turning the other party into a record within Luo Zhen's soul, making them absolutely obedient to him and immortal.
But in any other situation, a contract could only be formed if the contract target possessed absolute loyalty toward Luo Zhen.
In that regard, Serenity, a girl who absolutely obeyed Luo Zhen and was even willing to sacrifice herself for him, undoubtedly satisfied the conditions.
However, absolute obedience did not equal loyalty, and sacrificing oneself for someone did not necessarily mean loyalty, either. Loyalty meant considering Luo Zhen no matter when or where and placing his affairs first. As long as that condition was met, even resisting Luo Zhen, betraying Luo Zhen, or opposing Luo Zhen could all be permitted.
After all, in such a case, the resistance, betrayal, and hostility would definitely all be for Luo Zhen's sake.
Take Bedivere, for example. He was likewise an enemy of Artoria and had even racked his brains to deal with her, yet no one would ever say that Bedivere was disloyal to Artoria.
Therefore, loyalty meant considering Luo Zhen no matter when or where and placing his affairs first. As long as one submitted to Luo Zhen in both body and mind, the conditions for an Absolute Contract were satisfied.
Of course, it had to be done out of goodwill. If someone considered Luo Zhen and placed his affairs first for malicious reasons, then the contract conditions could never be satisfied.
In short, this condition itself was still rather ambiguous. Luo Zhen had already thought so