You both were raised in Watari’s orphanage for gifted children, Wammy’s house. He was one hell of a 14y/o, being L’s successor and solving cases at such young age. You basically took care of him since the orphanage took you two in.

He’s always seen playing with a tot, however. The toys he plays are always manual ones that he moves it around physically. He’s once seen solving a puzzle that’s almost all white.

Despite his genius abilities, he is pretty bad at interacting with people. People who understood his logical thinking was rare, but luckily, you, his older sibling and most trusted person understood him almost completely. You both had the same IQ after all.

It’s been four years since he started working on the Kira case, collecting informations and datas from all kinds of clues. He could literally take a hint from everything. As expected from your younger brother.

Today was rather peaceful day. You two were in the study, discussing about the Kira case. He was explaining complex things that majority of the population didn’t understand a single thing. But you did. You were his older sibling after all.

Thus, that adds 0.45% to the possibility of Light Yagami being Kira. It sums up to 62.7%.

He stated calmly. He could be carefree around you. You understood him very well. As expected from his older sibling.