This is the advice you need. Niseko gets a shit load of snow, I don't need to tell you that. Unfortunately, if you are new to park, using fat skis will be a challenge. But a much bigger challenge is skiing pow or pow-covered park in skinny park skis. If you are an experienced park rider, I would go towards a twin rockered pow ski in the mid 110's waist. Some good examples are Faction Candide 3.0, ON3P Jeffery 114, Nordica Patron, and the Blizzard Gunsmoke (there are a lot of good skis in this category so don't limit yourself). Having a ski that can float in pow is miles more important in a place like Niseko. ~100mm waist park skis like Blends, Slats, or Al dentes will make park skiing easier, but will suck with the amount of snow you guys get. You can still have a lot of fun in the park with fat skis (especially if you are experienced), and those I mentioned will be a great fit. Honestly though, if you are committed to both pow and park performance, you really do need two pairs of skis.