Ralsei and Kris first meet when Kris and Susie arrive in the Kingdom of Darkness. Ralsei, hidden under a hood, tells the Prophecy of the Delta Rune, after which he reveals more of his appearance. While Susie doesn't believe the prophecy and leaves, Kris stays with Ralsei. Ralsei joins Kris and gives them a tutorial on how to encounter enemies, encouraging pacifism.
Kris and Ralsei continue their journey together, and are not separated from each other for a long timd. Eventually, they are joined by Susie, but she later decides to join Lancer as their enemy. Eventually, Ralsei and Kris get both Lancer and Susie in their team (although Lancer keeps enough distance). Lancer later sends the three to jail (this was due to him wanting to avoid having them face his father) and while Susie is in her own jail cell, Ralsei and Kris are in the same cell.
Kris and Ralsei separate after the King is defeated. Before Kris and Susie leave, Ralsei shows his true face and hopes he can see the two again.
Kris has the option to put a white ribbon on Ralsei. If Kris does that, Ralsei asks while blushing 'if he's cute'.
Kris has the option to hug Ralsei, which Ralsei appreciates and blushes from.
If Kris' stands close to Ralsei for a long period of time, Ralsei starts blushing.
Like other Deltarune exclusive ships, it does not have massive popularity, and has notably less fanart than Kris or Ralsei alone or Kris, Ralsei and Susie as a team. It is still one of the most popular Deltarune ships.
On AO3, it is the third most written romantic ship and fourth most written overall ship for the Deltarune fandom. It is the most popular romantic ship for both characters involved, as well as the most popular ship for Ralsei and second most popular for Kris (behind the non-romantic ship between Kris and Susie).