A Pokemon Mega Symphonia booster box is a Japanese product containing 30 booster packs, with each pack holding 5 random cards. It features exclusive Japanese artwork and is a sought-after item for collectors and competitive players who want cards not available in English sets. 
Box contents
Packs per box: 30 booster packs
Cards per pack: 5 cards 
Key features
Japanese exclusive: The set contains cards with unique Japanese-only artwork.
Collector's item: It is highly valued by collectors for its premium packaging and exclusive art.
Player value: Players can use the powerful new cards to enhance their decks.
Packaging: Boxes are typically sealed and shipped from Japan, with some sellers noting that minor box imperfections can occur