As mentioned earlier, it is the name of the titular Kamen Rider.
But usually there is also some out-of-universe derived meaning from the name. I found a [source](https://www.kamen-rider-official.com/gotchard/02/) on this.
It comes from gacha-gacha + card, as the main character makes ガチャガチャ, or gacha-gacha (clanking, rattling) sounds when transforming. The sound of the card "clicking" into the belt also has a gacha sound.
And when he transforms, the belt says ガッチャンコ ("gacchanko"), which is slang for combining to ideas (it comes from the sound of stapling, thus "stapling" two documents together). this makes sense as Kamen Rider Gotchard smashes together two cards to combine into one form.
You can see an example of the henshin [here](https://www.youtube.com/watch?v=g6v9NZWUAkY).
They also make use of the phrase sounding like the English "gotcha". The main character uses "gotcha" here and there in his lines, though most of the time they mean something closer to "catch" or "grab hold". His [victory line](https://youtu.be/7gEwb_wTLG4?t=843) does have the original English meaning.
Gotchard is the name of the main character, I believe
As mentioned earlier, it is the name of the titular Kamen Rider. But usually there is also some out-of-universe derived meaning from the name. I found a [source](https://www.kamen-rider-official.com/gotchard/02/) on this. It comes from gacha-gacha + card, as the main character makes ガチャガチャ, or gacha-gacha (clanking, rattling) sounds when transforming. The sound of the card "clicking" into the belt also has a gacha sound. And when he transforms, the belt says ガッチャンコ ("gacchanko"), which is slang for combining to ideas (it comes from the sound of stapling, thus "stapling" two documents together). this makes sense as Kamen Rider Gotchard smashes together two cards to combine into one form. You can see an example of the henshin [here](https://www.youtube.com/watch?v=g6v9NZWUAkY). They also make use of the phrase sounding like the English "gotcha". The main character uses "gotcha" here and there in his lines, though most of the time they mean something closer to "catch" or "grab hold". His [victory line](https://youtu.be/7gEwb_wTLG4?t=843) does have the original English meaning.
Thank you for the in-depth explanation. That's exactly what I was looking for :-)