On 7th, I met Yokohama Minatomirai Railway Y500 Series in a rapid express service bound for Ikebukuro on Seibu Ikebukuro Line due to the delay on Tokyo Metro Yurakucho and Fukutoshin Lines which the platform screen door check caused.
The going-through service between Yurakucho and Fukutoshin Lines and Seibu Ikebukuro Line temporary suspended and the operations by Tokyo Metro, Tokyu, and Yokohama Minatomirai Railway carriage changed their destination to Ikebukuro from their original ones.
Y500 Series exists only six 8-carriage sets (one set were out of order because of an accident in 2014), it is hard to distinguish which operation it is used because it is regarded as the same as 8-carriage Tokyu 5050 Series, and 8-carriage set rarely is in rapid express service.
As usual, rapid express trains for Ikebukuro don't stop at Nerima, but it did there because it operated as the one instead of the going-through service train.