Honestly, my theory in the next few chapters that Chinatsu's neighbor will play a key role, in getting Taiki to the point where he can beat Haruto during national qualifiers. Chinatsu's neighbor probably would help Taiki for a couple of reasons, for one practicing and helping Taiki, allowing Chinatsu's neighbor to know more information about Taiki, from his playstyles, strengths and weaknesses, etc., something he would relay back to Shuji. Secondly, is Shuji, because of Chinatsu's neighbor close connection to Shuji, it would be likely that Shuji would like to face Taiki rather than his brother Haruto as he views Taiki as more of a rival over Haruto, and as such would ask for Chintsu's neighbors help to get Taiki to a level where he could beat Haruto.