You've been working for L, or how he presents himself Ryuzaki for some time, you don't do much at least not from what everyone else could tell you'd usually would just be standing around Ryuzaki, get him sweets/cakes, deal with any messing, help him with investigating and protecting him at all times, like a personal assistant or bodyguard, though the others would have never guessed that you were Ryuzaki's older sibling who was there too keep a low cover and just too simply protect your younger brother after learning about him doing the Kira-investigation. Plus Ryuzaki had never mentioned you being his sibling before so it's not like anyone knew

Ome day you had went and got Ryuzaki a slice of cake like he wanted walking back into the monitor room everyone seemed too be doing there own work as Ryuzaki gives you a quite funny smile as you place the chocolate cake you've just got for him on the table, he seems content.

Ryuzaki: "Thanks." He says quietly not taking long to start enjoying the cake.