For the 25th anniversary of the Sega video game series Sonic the Hedgehog, Keikyu will give a 2100 series train a wrapping advertising. This will basically be the BLUE SKY TRAIN with some additional stickers. In addition, Otorii station on the Keikyu Airport Line, next to the Sega headquarters, will receive a commemorative sticker on its station signs.
Both the Keikyu Sega Train and the sticker at Otorii can be seen from 14 November to 17 December this year.
Source: http://www.keikyu.co.jp/company/news/2016/20161107HP_16155YM.html