To celebrate SID's 15th anniversary , SID 15th Anniversary Calendar 2018 (cost - ￥2,500) will be released beginning of April
A set of 4 postcards will be given as an external bonus item for early preorders
https://twitter.com/sid_staff/status/970584709876142080
http://shopping.deli-a.jp/products/i...hp?itemID=9824