You know the saying "Speak of the devil and he will appear"?
Kohaku said he dislikes the retainer of the blue monarch (another mystical beast like Kohaku himself - the blue dragon).
So my bet is that this new dragon is the retainer Kohaku spoke of and the retainer noticed Kohaku's presence and came or he was told to go there by the blue monarch who noticed Kohaku.
@mageexia bad anime adaptation and bad reception then became a meme of a shitty series. The manga's pacing and details are better than the anime but all in all, it's still a generic decent lighthearted series.
I already accepted the levels of mediocrity this story tries to sustain, but it's really underwhelming how the MC is presented as a container of unlimited power, and he only uses "level 1 spells". Even if it's to maintain the harem's image of "strong female warriors", making the MC weaker than he should be, so the girls' have presentable merit, is pretty weak.
This is one of those things that really surprised me that it sold at all.
@Miradante
Honestly, the MC doesn't even need the other elements. If anything, it's a problem he even tries to directly attack anything, when he can just crush anyone's heart from afar, or paralyze them and have his harem bash them afterwards. The issue is that the MC does not trivialize every single mob he encounters, since everyone should practically be 100 levels below him.
@Talh - the way I understand is, all white tigers are retainers of Kohaku the White Tiger, and all dragons are retainers of Seiryuu the Dragon. Even if they don't know that.
@Miradante - Slip is the ultimate magic. Good for defeating anything from corrupt nobles to sealed ancient evil. Touya loves it so much he should marry it.
Light magic is just suitable to demonstrate his majesty. It probably also doesn't explode, and hits exactly what Touya wants.
@Solipsist - I think you're confusing this series with Death March. Isekai Smartphone doesn't have levels.