From OUT magazine for August (pp. 13-4), a feature on the music world (“On a Mi(ssion): Cody Critcheloe has a high-concept queer art project with a beat” by Adam Rathe):
The name, copped from Boston post-punk pioneers Mission of Burma, sounds like shun, but bewilderment regarding how exactly to talk about the group – and people are talking — is just part of Critcheloe’s plan.
“I love the name, how it looks, and how it’s confusing for people,” he says. “I love that people can’t pronounce it or that they think it’s my name.”
Of course it’s confusing; it makes a name out of an unaccented syllable that isn’t in itself meaningful — but sounds like an existing English word. And it’s weirdly spelled.
A bit more on the band, from Wikipedia:
The Ssion, also known as SSION, (pronounced “shun”) is a musical group formed in 1996, in Kansas City, by vocalist Cody Critcheloe. Known for their extravagant live show, Ssion was signed to Sleazetone Records in 2008.
In 2003 Ssion made their label debut in 2003, releasing the EP “Minor Treat” and the album “Opportunity Bless My Soul” on Version City Records. In 2007 the group released their album “Fools Gold” accompanied with “Clown”, a remix EP. It was then followed by a full-length feature film, titled BOY made up of music videos strung together to produce the gay, punk rock equivalent of Forrest Gump.
There have been several bands named Shun, for instance this one:
Shun has been a band for around four years, and throughout those years they have learned what it takes to try and make a stand in a hard business
… Shun has played many shows covering the southeast from Nashville to New Orleans, playing with many known bands such as The Urge, Stuck Mojo, and Nothingface.
But Ssion / ssion / SSION is extravagantly queer. Here’s a relatively restrained publicity photo (that’s Critcheloe in the mustache):
And a bit from a live performance, here.
Now about getting /ʃʌn/ from mission. For most speakers of English, mission is simply an unanalyzable word, so /ʃʌn/ is just what you get when you chop off the second (unaccented) syllable and give it accent. This second syllable has no meaning on its own, certainly nothing to do with shunning.
Now, it’s true that that syllable has a history — the etymology of mission goes back to the Latin mit- ‘send’ root and Latin material ending up as an -ion nominalizing suffix in English (cf. rebel – rebellion) — but that history is complex (the /ʃ/ represents a fusion of the /t/ in the root and the /j/ < /i/ in the affix) and dead to all modern speakers except the few who take an academic interest in English etymology (who will appreciate the parallel to the morphophonological alternation in permit – permission and similar pairs). But now /ʃʌn/ has risen, ripped out of mission for Cody Critcheloe’s playful purposes.