Out of all the instruments that are available, you decided that you should play the microphone in order to get the door open, and before you start playing the microphone you make sure that it's plugged in, despite there probably not being any power in the building, due to the apocalypse and all. However, you are left completely baffled as the microphone receives power. Now, normally you'd be put off by the power present in the building and it's outlets, but you deduce that it could be coming from a backup generator, which lessens your worries. Now that your microphone has some power, you take it off the stand and begin to sing...
(The song your singing here doesn't matter to this story, so let's get into the transformation.)
As you begin to to sing into the microphone your body begins to shrink down to the height of an octoling woman, but you don't notice it as you are too distracted by your own singing. The next thing to change while you are singing is the movement of the fat in your body, or more specifically, your body fat moving to your upper chest giving you sexy B cup breasts, and the rest of said body fat moves to your rear, giving you a beautiful dump truck ass. Afterwards, your physical body shape changes as well to a absolutely perfect hourglass figure that'll definitely arouse anyone that sees it. This is followed by your skin becoming as soft as silk, and your facial feature become more feminine as octoling-esque, even featuring the pointed eyes that you see on female octolings. Next, your hair elongates down the majority of your back before it turns into some smooth octoling tentacles, one of which covers your eye. "Ever since I began my singing career, I've always emphasized that one of my tentacles must cover my eye, and my audience loves every second of it, oh veemo," you think to yourself before quickly coming to your senses. "Wait, I'm not a singer, why was I thinking that, AND WHY CAN'T I STOP SINGING?!" After realizing this you can only watch as you, now a prisoner in your own body, witnesses the transformation finish before being wiped from existence entirely, speaking of which...
After you sexy octoling tentacles finish forming, your voice begins to seamlessly change into that of a sexy octoling singer's, which will surely attract and arouse all of your adult fans. Finally your penis and testicles go into your body before turning into ovaries and a vagina, and with that, all of your prior memories are erased, with brand new ones forming in their place...
Now, with your new set of memories, you finish your singing rehearsal and think to yourself, "Veemo, that was an incredible singing rehearsal! If the main performance goes like this the fans will love it! I can't wait!" You then finish your thought as the PA system announces, "Rehearsal Over, doors to the main stage have been unlocked." "Well that's my que, better head to the stage" you state as you head through the doors; giving an incredible performance to all of your sexy female inkling and octoling fans.