Complex sentence: He decides to boycott the team's "official" Matsuki and create your own... which after a first and illusory victory will always be defeated by that of Matsuki, which begins to be seen by Shingo as an invincible enemy.
Split into simpler sentences: He decides to boycott the team's "official" Matsuki team and creates his own. After a first victory, he is always defeated by that of Matsuki, which begins to be seen by Shingo as an invincible enemy.