'merciful towards' is correct and usable in written English
You can use it when speaking or writing about someone or something being compassionate or forgiving. For example, "The teacher was merciful towards the student and gave her another chance to pass the test."
Hayes was apparently very merciful towards Paraguay after taking charge of peace talks after the War of the Triple Alliance (which sounds like it should be in Star Wars, but was actually an exceptionally bloody affair in the 1860s involving Paraguay, Argentina, Uruguay and Brazil).
While the former was dashing, ruthless and brave to the point of absurdity, the latter was humble, pious and relatively merciful towards those he vanquished.
Although it was not known how devastating the explosions and the aftermath would be, Truman, like most Americans, was not inclined to be merciful towards the Japanese in the wake of the long years of war.
To underscore his point, Lee went on cite the Attorney General's April comments about New York City's gang murders being the result of NYPD's being merciful towards it stance on crime.
Officially it considers same-sex unions "an error," but Pope Francis said last month that lawmakers "should never forget the necessary, merciful love towards people who, as a free choice or as a result of unlucky life circumstances, live" in that state of error.
Nikola is portrayed in East Slavic folklore as merciful and protective towards the common people, patron of animals and agriculture, connected with riches, abundance, and fertility.
"But if you knew that the most common prayer in Islam is 'In the name of God, the all merciful,' your attitude towards Muslims would probably be a lot better".
Francis, who says he wants his Church of 1.2 billion members to be more merciful and less rigid towards sinners, said the Jubilee would be an occasion for all members - and the Church itself - to rediscover the need to be forgiving and generous.
Blessed are the merciful, for they shall obtain mercy.
"Blessed are the merciful, for they shall receive mercy".
The prize, in 1823, for William's agreeing to swear an affidavit as to the merciful behaviour of Sir Hudson and the British cabinet towards Napoleon, was that William would be given a government job.
