He is Saotome Kazuya's next door neighbour. He sometimes make huge crushing sounds causing Kasumi to run back to chase him for the rent. He also helps to provide ice blocks for Kasumi to lower the temperature of the cyberdolls in Episode 10. He shows up again with no appearance but with crushing sounds in the Last Episode. It also seems only Kasumi and May saw his appearance. The name Shikishima might be a reference to Professor Shikishima of Tetsujin 28 and the crushing sounds might be the attempts Shikishima trying to rebuild Tetsujin. After the credits in episode 10, it is hinted that Shikishima has possibly finished rebuilding Tetsujin.

(Source: Wikipedia)