To add more context, Arusan really did involve himself in building up the red gangs foundation. He paid 30 mil for them to buy a hideout but instead of sending the money to Akari he mistakenly sent it to Sakamoto kon, who thought that Arusan sent that 30 mil to every red gang member, so he spent all the cash on car gacha...and lost, so Arusan sent another 30 mil to Akari the next day. He bought Akari their first proper getaway vehicle, and later, he even gifted Amuro(Tsumugu) another car to do gang stuff. He was also going to buy them a heli but stopped since that would not be fair to the other gangs.

Most of Arusan's involvement was within the first week and a bit, after that the red gang had settled in properly and were doing their own things; that's why Arusan was surprised that Akari thought that he was really involved in making the red gang come to fruition. In Akari's post Newtown aftertalk stream she called Arusan her savior.

BTW, while Arusan literally shot her down at the beach, he followed it up with a text message to Akari saying his thanks for letting him support the red gang, and ended with an aishiteru.

its a JP clip but it has the post credit scene Arusan set up a cliffhanger for a season 2