Fate/stay night, C: The Money of Soul and Possibility Control Recommendations
Assets are like Servants and the people in the Financial district (Entre's) are like Masters. Both anime's have people who has servants/assets who fight for them and are summoned when needed to. Similarly both have the main character showing compassion and care towards their servant/asset and trying to help them in fights/duels.
Both young male main characters with a female partner (asset) and they fight to protect those close to them and whats important. They struggle through their battles but show great potential and determination.
Main characters are very similar, especially in their initial indecisiveness and the development of their relationship with the female lead. Overall, Assets = Servants, Entres = Masters, Holy Grail War battles = Financial District deals. The set-up is also very similar with the relationship between the protagonist and the antagonist with the main villain or anti-hero giving the hero his reason to fight. Also, both series eschew black-and-white morality for a more complicated battle between parties who each have reasonable and nuanced motivations and values.
The life of a normal high school student is thrown upside down when he is given a girl of some sort to fight for him against people who have other people to fight for them. In C if he loses the fight he loses money and in Fate/stay night if he loses the fight he loses his life.