I just thought of something.

Everyone always wonders about how they know that someone won’t come back to life if they die during a XANA attack.

What if Yumi had another younger brother and at some point between XANA Awakens and Teddygozilla, that brother died and the return trip didn’t bring him back so Yumi’s family adopted Hiroki and that’s why Yumi’s always so worried when a XANA attack involves Hiroki.