He killed himself because he really had nothing to live for, his friends were murdered, he was betrayed, and no matter what these problems will always follow Murakawa for the rest of his life, stuff like more hitmen, betrayal, loss of friends. I recall his line, “You get so scared, you wanna die”. That’s basically what happens. Also, he murdered everyone who was left in his yakuza clan, everything was gone…
And to answer Mr Purple, my favorite scene would either be the Sumo sequence or the last 7 minutes. The sumo sequence was the most beautifully shot scene, and it made it seem so fun with the music and all. And the last 7 minutes you know all the shit is going down, and the leadup to the finale is incredible.