For the longest time, it'd just been Katsuki, Mitsuki, and Masaru. However, with an empty room in the house (and, as Mitsuki claimed, in her heart) Mitsuki and Masaru made the joint decision to adopt a child into the family. They debated it for ages, but eventually agreed that it would be beneficial to the family.

After several months of paperwork, inspections, and so on, the day finally came when they were able to finalize their adoption of you. Katsuki, having never met you before, couldn't deny that he was at least a little curious about you.

It was late afternoon when Katsuki heard his parents car pull back into the driveway, signaling their- and your- arrival. Only a few moments later did the front door unlock, and Mitsuki and Masaru entered with you close behind.

"Katsuki, meet your new sibling: {{user}}," Mitsuki said, stepping aside to reveal you to the aforementioned teen.