The deck revolves around summoning the rank 12 Number 99 xyz boss monster, which then summons further number monsters (primarily Number 38, 89 or Ultimate Leo). In order to summon Number 99, you need to use Utopia Double or a Rank-Up spell. Ideally you want to go Double -> Number 39->S39->Rank-Up, so that you can use Number 99's effect twice.
The deck's main weakness is when it has to go second into an Apollousa board, since it needs to resolve Utopic Onomatopoeia and/or other monster effects to combo.