• At Level 10, "Koitsu" has the highest level of all Union Monsters and WATER monsters. It also has the highest ATK increase in its effect for its host, "Aitsu".
  • Aitsu, Koitsu, Soitsu and Doitsu are from Sexy Parodius, a Konami game that parodies Gradius.
    • When translated, the names mean "That Other Guy", "This Guy", "That Guy" and "Which Guy?" respectively. The names are whimsical, and are not meant to be taken literally.
  • "Aitsu", and "Koitsu" make an appearance in Konami's Castlevania: Harmony of Despair when a player controlling the character Jonathan Morris uses the subweapon, "Paper Airplane" at a higher level. At level 5-8, only one person can be seen riding the airplane. But at max level (9) both "Aitsu" and "Koitsu" can be seen riding on the plane.

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