Open responses to 1.d4 and 1.e4?

I'm new to chess and trying to establish an opening repertoire.  I've settled on the KIA for white, and I'd like to play something in a similar style as black. I want a somewhat open/tactical position where I can attack and make threats depending on white's structure. I don't mind some theory but I would prefer if the game becomes free-form reasonably quickly. I've looked into the KID, Scandinavian, and Dutch but I'm not sure if those would suit me very well so I'm still undecided.

There's some confusion with the terminology here... the KIA is not open, but it is something you can play based on knowledge of structures, which in turn is not "free-form" (like a tactical melee).

I think the Scandinavian is a good choice for newer players because it gives white very little chance to deviate (you make it the Scandinavian on move 1). It also opens some lines so it's not a long confusing maneuvering middlegame.

But... I'm still not exactly sure what you want, so it's hard to give suggestions.

Ah ok, an opening setup that you can (more or less) do against anything is called a system. The KIA is a system. The London and stonewall and some other things can be called systems.

Umm, it's kind of hard to know what information to give you and what to leave out. For example the KID setup isn't really a system as black because if white has played e4 then it's an opening that's called the Pirc. Is that useful information to give you when you're new and just looking for a set of moves to reliably get you to move 10 with a reasonable position? I don't know... so I'm mentioning it like this to let you know both that this information exists, and also that you can probably ignore it haha

In a similar way, a semi-slav setup is sort of a system against 1.d4. The hedgehog is sort of a system against 1.e4. Playing the London but with black might be called a system (this is a useful default when facing a flank opening you're unsure how to deal with e.g. 1.g3).

These are all options that will reliably get you to move 10 with at least an equal position for now. As you get better you'll want to look into them a little more.

Also, that was the direct answer to your question.

Some people might take a more indirect approach and point out telling a near-beginner to "play the hedgehog against 1.e4" is not great advice. Some might even tell you systems in general are bad, or that openings in general aren't worth worrying about.

All of that is also reasonable advice, but #4 is my attempt to answer the question at face value.

If you want something against a lot of stuff, perhaps the modern? You can play it against almost anything. lol

The Modern will usually transpose into a KID or Pirc. It's just 1.e4 g6 after all.

If you play the King's Indian Attack as white, then the King's Indian Defence as black is most logical. By the same reasoning Pirc Defence is most like King's Indian Defence.

They lead to wildly different position so...

But yes, in the eyes of a total beginner they're very similar.

Actually, most Modern Defense players do not transpose to the KID or Pirc and either delay the development of the g8-knight or else move it to e7 rather than f6.

The Pirc Defense and the King's Indian Defense are NOTHING alike!

That c-pawn for White makes a HUGE difference.

In the Pirc, after 1.e4 d6 2.d4 Nf6 3.Nc3 g6 4.Nf3 Bg7 5.Be2, the only thing covering the e-pawn is the c3-Knight.  Black will usually play 5...c6 and 6...b5, threatening ...b4 to dislodge the knight and win the e-pawn.  Obviously White will do something about that cheap shot, but the attack continues to be on the e4-pawn.

In the King's Indian, 1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.e4 d6 5.Nf3 O-O 6.Be2, the White c-pawn is on c4 rather than c2.  This makes the d4-square permanently weak because e4 and c4 have both been played, so no c3 or e3 to guard d4.  Also, c6 and b5 going for b4 is impossible here because of the white c-pawn.  So going for e4 is impossible.  The attack is on d4 and the dark squares as a whole.

Comparing the Pirc to the King's Indian is like comparing a Tuxedo to a Bikini.  Both are articles of clothing.  The Pirc and KID both see a fianchettoed Bishop and pawn on d6.  That is literally all they have in common.

The King Pawn opening most similar to the Kings Indian is the French.  Blocked center with play on the wings and pawn chains are the theme of both openings.  The direction the blocked pawns point is the direction you attack.  French is a kingside attack for White and Queenside attack for Black.  King's Indian is just the opposite with the exact same ideas.

The QP opening most similar to the Pirc, with an attack on e4, is probably the Modern Benoni or the Grunfeld (the Grunfeld being more similar to facing the Austrian Attack where Black is forced to chip at White's center and trying to get him to over-extend.

The Pirc and KID are nothing alike!

Don't do it. It takes many, many hours and it would be an almost complete waste of time. Those hours are much better spent is you solve tactics puzzles. Or read a chess book. Or watch some videos about some great players of the past.

If you want to improve, you don't need an opening repertoire. What you need is to improve your calculation skills and get better at tactics. So in short, you need this:

https://www.chess.com/puzzles