Marakei is a small atoll in Kiribati's Gilbert Islands chain, and remoteness is not a side note here - it is essentially the whole story behind why travel insurance matters. There is no dramatic danger particular to Marakei; the honest risk is that almost nothing serious can be handled on the atoll itself, and everything depends on how quickly and reliably you can leave it.
Marakei has only the most basic local health services, adequate for minor complaints but not for anything beyond that. Serious illness or injury is typically stabilized if possible and then evacuated first to South Tarawa, Kiribati's capital atoll and the country's main hospital, and from there, if specialist treatment is needed, on to Suva, Fiji, the regional referral hub for much of the Pacific. Confirm your policy explicitly covers inter-island evacuation within Kiribati as well as international medical transfer, since a policy limited to local treatment misses both legs of what a real emergency here actually looks like.
Inter-island transport to and from Marakei itself is limited and irregular, typically by small boat or light aircraft depending on the route, and schedules can slip for reasons ranging from weather to simple availability. This is worth planning around regardless of the activity on your itinerary, since even a routine return trip can be delayed for reasons entirely outside your control. Cyclones rarely track this far north in the Pacific, given Kiribati's near-equatorial position, but rough seas and unpredictable inter-island transport are the more everyday disruption to expect here.
Keep any clinic paperwork from Tarawa or wherever you are treated, records of inter-island transport arrangements, and receipts for any emergency transfer, since documentation from a place this remote is easy to lose track of and hard to reconstruct later. Check the claims process in your policy wording for evacuation specifically before you travel, since Marakei is about as far as this guide gets from a straightforward emergency-care picture.