Hello everybody!

For some time now I'm looking for an old arcade game.

I remember clearly playing it several times around 1990.

It was a side-scrolling arcade game in which you control a ninja, much like Cadash (yet, here you just have the ninja and it is a strictly 1-player game).

The ninja shoots shurikens to kill enemies and I remember that keeping the attack button pressed allowed to unleash more powerful attacks, such as fireballs and earthquakes.
I also remember you are able to power-up the ninja by getting scrolls.

The ninja did not have a cape, he was much similar to the ones seen in Legend of Cage or Ninja Spirit.

Could you help me identifying this game?

Sounds like Shadow Dancer
Did you look through all the Arcade longplays already?

No, it was not Shadow Dancer or one of the other "main" ninja arcade games. :)

I've searched throught the list of the arcade lognplays and did not find it.

As an additional information, the attack-charging mechanic is identical to the one seen in Capcom's Willow: the longer you keep the button pressed, the more powerful the spell cast is.