Just a good, colorful bento guest that, though I have never tasted, is enjoyed very well by my husband!
Tips and tricks
I've done this many times without mirin and I think it was fine. I have no idea between the difference in taste, anyway. ^_^;
Another version of tamagoyaki that earned a voluntary "the egg today was delicious" comment from my husband was when I used small bits of eggplant (instead of carrot and bell pepper), a bit of milk (instead of mirin) and cheese slice (instead of nori).
I've had better days with tamagoyaki rolling but I didn't have a chance to do a pictorial aside from when they were already in my husband's bento box:
A vegetarian for 12 years and a kitchen warrior since I moved in to Japan, my favorite battle has been winning over my husband's interestingly complicated taste buds.