The Lasstranaut t-shirt was originally to be included as a bonus in any Tomorrow Kings Oyabuns package. ThreeA delayed the release of the shirt so that they could re-print it and get the colours right, but decided to ship the Oyabuns regardless with a sticker that promised the t-shirt would ship as soon as it was ready. The t-shirt is designed after the same one sported by the Oyabuns and was shipped in the vinyl Bertie Container.
Quote off the Production Blog: "As you guys are gonna have these in hand as of this week and beyond, here it is the Bertie t-shirt container all its glory, with Lasstranaut T inside ! We are going to offer some cool shirts soon, such as the mythic 1/1 Tomorrow King boxed t-shirt collection." source