Heading from Boulder to Basalt, Sun Jr. will hit the stage at 8 p.m. on May 9 at The Arts Campus at Willits. The part-time band broke out when its 2024 single release “Buttercorn” went viral. “We had a weird situation happen that we weren’t really ready for,” bandmember Jon Schimek said. “We had a song go viral on TikTok, ‘Buttercorn,’ with 2.5 million views.” Schimek admits he was surprised at how many more people said “hi” after the buzz — wh…