Is this a good mousepad for competitive gaming?

It is a printed desk mat with edge lighting, not a tournament pad. It is fine for casual play; serious players usually pick a plain low-friction cloth surface.

How is the RGB lighting powered?

LED edge pads like this run off USB power, so you need a free USB port or adapter nearby. The light is decorative and does not affect mouse tracking.

Can I use it under my keyboard too?

Yes. The mat format is sized to sit under a keyboard and mouse together, which is the usual way to use a desk mat.

Will the printed artwork fade?

Printed cloth pads can show wear over time, especially where the mouse moves most. Keeping it clean and out of direct sun helps it last.

Is it a good gift for a Kiriko fan?

It is aimed at exactly that: a themed, lit desk mat for someone who plays Kiriko. It is a decor piece first, so pick it for the look rather than for pro-level performance.