Is forgiveness a fruit of evil wicked kamma? I read the following on the internet:


  Yet there were still a few who could not forget that Angulimala the
  bandit, with his superior prowess, had shown them in their weakness
  and thus had humiliated them. Out of that resentment, as an act of
  revenge, they were mean enough to injure the venerable Angulimala by
  throwing stones and sticks which struck him when he had gone for alms.
  They must have done so from a safe distance.
  
  Then with blood running from his injured head, with his bowl broken,
  and with his patchwork robe torn, the venerable Angulimala went to the
  Blessed One. The Blessed One saw him coming, and he told him: "Bear
  it, brahmana, bear it, brahmana! You have experienced here and now the
  ripening of kamma whose ripening you might have experienced in hell
  over many a year, many a century, many a millennium."
  
  Being a saint, his mind and heart were firm and invulnerable. But the
  body, the product of former craving, the symbol and fruit of previous
  kamma, was still there in present existence and was still exposed to
  the effects of former evil deeds. Even to the Buddha himself it
  happened that, as a result of former deeds, Devadatta was able to
  cause him a slight injury. Also his two chief disciples had to
  experience bodily violence. The venerable Sariputta had been hit on
  the head by a mischievous demon, and the venerable Maha-Moggallana was
  even cruelly murdered. If this occurred in the case of these three
  Great Ones, how could Angulimala have fully avoided bodily harm — he
  who in his present life had committed so much evil! Yet, it was only
  his body that received these blows, but not his mind. That remained in
  invulnerable equipoise.


In the sutta about Angulimala, King Pasenadi forgave Angulimala of his evil deeds. The sutta says:


  "Great king, suppose you were to see Angulimala with his hair &amp; beard
  shaved off, wearing the ochre robe, having gone forth from the home
  life into homelessness, refraining from killing living beings,
  refraining from taking what is not given, refraining from telling
  lies, living the holy life on one meal a day, virtuous &amp; of fine
  character: what would you do to him?"
  
  "We would bow down to him, lord, or rise up to greet him, or offer him
  a seat, or offer him robes, almsfood, lodgings, or medicinal
  requisites for curing illness; or we would arrange a lawful guard,
  protection, &amp; defense. But how could there be such virtue &amp; restraint
  in an unvirtuous, evil character?"
  
  Now at that time Ven. Angulimala was sitting not far from the Blessed
  One. So the Blessed One, pointing with his right arm, said to King
  Pasenadi Kosala, "That, great king, is Angulimala." Then King Pasenadi
  Kosala was frightened, terrified, his hair standing on end. So the
  Blessed One, sensing the king's fear &amp; hair-raising awe, said to him,
  "Don't be afraid, great king. Don't be afraid. He poses no danger to
  you."
  
  So King Pasenadi Kosala went to the Blessed One and on arrival, having
  bowed down, sat to one side. As he was sitting there he said to the
  Blessed One, "It's amazing, lord. It's astounding, how the Blessed One
  has tamed the untamed, pacified the unpeaceful, and brought to
  Unbinding those who were not unbound. For what we could not tame even
  with blunt or bladed weapons, the Blessed One has tamed without blunt
  or bladed weapons. Now, lord, we must go. Many are our duties, many
  our responsibilities."


Was the forgiveness of King Pasenadi Kosala towards Angulimala a fruit or product of the old evil kamma of Angulimala? 

Since the suttas say "kamma is intention", did Angulimala "will" the forgiveness from King Pasenadi Kosala; similar to how a sexy lady may intentionally seduce a man?
Was the forgiveness of King Pasenadi Kosala towards Angulimala a fruit or product of the old evil kamma of Angulimala?

The king's initial fright appears to be a consequence of Angulimala's evil deeds.

The king's forgiveness appears to be a consequence of Angulimala's being tamed.

The king's believing what the Buddha said was -- I'd guess -- perhaps a consequence of the Buddha's earned reputation for speaking truthfully, as well as, his seeing for himself with his own eyes.

Since the suttas say "kamma is intention", did Angulimala "will" the forgiveness from King Pasenadi Kosala; similar to how a sexy lady may intentionally seduce a man?

Are you kidding?

Angulimala's "intention" is perhaps as described by the Buddha:


  Angulimala [is and intends to be]  with his hair &amp; beard shaved off, wearing the ochre robe, having gone forth from the home life into homelessness, refraining from killing living beings, refraining from taking what is not given, refraining from telling lies, living the holy life on one meal a day, virtuous &amp; of fine character


... and ...


  [one who] poses no danger to you


I also tried to find what Angulimala's root intention or original intention was -- why was he like that now?

According to Angulimala -- A Murderer's Road to Sainthood (which you're quoting in the question), here is what that said about and quoted by Angulimala at the moment of his "conversion":


  
    (The Blessed One:)
    
    "Angulimala, I have stopped for ever,
    Foreswearing violence to every living being;
    But you have no restraint towards things that breathe;
    So that is why I have stopped and you have not."
  
  
  When Angulimala heard these words, a second and greater change of heart came over him. He felt as if the current of his suppressed nobler and purer urges had broken through the dam of hardened cruelty that had been built up through habituation in all those last years of his life. Angulimala felt now deeply moved by the appearance and the words of the Buddha.
  
  Angulimala's response and what followed is again tersely told in the Sutta:
  
  
    (Angulimala:)
    
    "Oh, at long last a sage revered by me,
    This monk, has now appeared in the great forest;
    Indeed, I will for sure renounce all evil,
    Hearing your stanzas showing the Dhamma."
  


His intention appears to be motivated by reverence for the sage and renouncing evil.

What you ask may be partially true though -- an advertised benefit of the (ethical) precepts is that they provide safety (and so freedom-from-fear, I presume) to all beings -- to that extent (i.e. it's because of those consequences) an intention to keep the precepts may include that intention to affect the minds of others or to share the benefit (goodwill and so on).

It's probably not supposed to be deceitful or impermanent though, e.g. in the way that "seduction" which you referenced is often portrayed to be.

And I think the effects of kamma aren't simple and singular, they interact:


I suppose there are many ways to describe his motive and intention -- e.g. "he does it because he knows what good and evil are"; or "because he sees the Buddha's good example"; or "for his own peace of mind"; etc.
Similarly the effects of kamma are numerous -- affecting himself, the king, and others.
And each person's actions are affected by multiple causes -- the king's forgiveness being affected by not only Angulimala but also by the Buddha, and the king's own ability.