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Though the two have never met each other in canon, Tsumugi's favorite character in the entire Danganronpa series Is Junko, idolizing her very much and wishing to continue the Killing Game she created, forcing 16 students to participate.
At the end of the 5th class trial, Tsumugi secretly went to the hidden room, and cosplayed as Junko, to confuse the viewers. Stating that The Killing game will continue on as long as she’s alive.
At the 6th class trial, Tsumugi is revealed to be the mastermind. Panicking, she claims that Junko Enoshima is the mastermind once again because it's always been her. Though only a few moments later, realizing she has been caught, Tsumugi drops her act, and claims herself as “Junko Enoshima the 53rd, The Ultimate Despair” Though she is only cosplaying as Junko, she went on saying that she only wanted to repeat her killing game once again and claiming that there is no audience to it.
- “It’s Junko Enoshima Cuz... it’s always been her.”
- — Tsumugi claiming that she couldn't have been the mastermind because it’s always Junko.
- “Junko... Enoshima is… Right the fuck here!”
- — Tsumugi revealing herself as "Junko Enoshima the 53rd"
The ship sailed as a result of Tsumugi strongly idolizing Junko and wanting to spread Despair herself. Because of Junko, Tsumugi was planing her own Killing Game that she then later also started. Some people like to imagine what would have happened if Junko and Tsumugi would have met in canon. Many like to imagine that if Junko and Tsumugi would have met, they would have become 'Partners in Crime' together. Tsumugi cosplaying as Junko and acting like Junko in the final Trial also helped it's case.
There are a few similarities between Junko and Tsumugi, both were the Mastermind of a Killing Game (Junko was the Mastermind of the first and second Danganronpa Games and Tsumugi was the one of the thrid game). Both also have an Obsession with Despair and used the Killing Game and recorded it to spread Despair among the World. Junko and Tsumugi also both had people that they needed to get of the way, because they considered them a burden for the Killing Game, for Junko it was Kyoko Kirigri and Makoto Naegi, and for Tsumugi, Kaede Akamatsu and Rantaro Amami, but unlike Junko, Tsumugi successfully got rid of the two.
Noneless, the ship is semi-popular in the fandom, both Junko and Tsumugi have more popular ship's like Shironaga and Junkan, which highly overshadow Shiroshima, but it's also not considered a rare-pair among the fandom, which is a suprise since Junko and Tsumugi have never met in canon. Fan fictions often portray their relationship as it is in canon, Tsumugi is admiring and idolizing Junko and sometimes fan fictions also include a romantic relationship between the two. On Archive Of Our Own the ship has currently 37 fan fictions, which is a lot for such a minor ship.
- Both Junko and Tsumugi are masterminds of multiple killing games.