Stormchaser Drake solely triggers on being focused by a spell. Ninjutsu is neither a spell, nor does it goal something.

First, Stormchaser Drake solely triggers when it’s focused by a spell, however Ninjutsu is a capability. You activate it out of your hand superficially much like a spell, however that does not make it a spell.

112.1. A spell is a card on the stack. [..]

702.49a Ninjutsu is an activated skill that capabilities solely whereas the cardboard with ninjutsu is in a participant’s hand. [..]

Second, Stormchaser Drake solely triggers when it’s focused by a spell. Being focused has an outlined which means in Magic. If a spell or skill doesn’t have the phrase “goal” in its textual content someplace, it doesn’t goal something (besides aura spells, which at all times goal one thing) and may’t set off Stormchaser Drake.

115.1a An immediate or sorcery spell is focused if its spell skill identifies one thing it is going to have an effect on by utilizing the phrase “target [something],” the place the “something” is a phrase that describes an object and/or participant. Ninjutsu doesn’t have the phrase “goal” in its textual content, so it does not goal the creature it returns.

702.49a [..] “Ninjutsu [cost]” means “[Cost], Reveal this card from your hand, Return an unblocked attacking creature you control to its owner’s hand: Put this card onto the battlefield from your hand tapped and attacking.”