Responses
Because "older brother"(shigure) wanted to sneak shiro out-like leaving the yazuka..? But he knew too about the dark deeds he was made to do so they killed him. Then haru blamed himself because he introduced shiro to older brother. If he didn't introduced shiro to older brother (shigure) he wouldn't have decided to leave and he wouldn't have been killed.
Why haru said that because of him introducing Shiro to "older brother" that why he get killed?