[TOMT][Cartoon][2010s] Animated Show about collecting Monsters

Further Setting details:

-I watched it in Germany on Nickelodeon/ Kika/ Disney Channel / Super RTL or Cartoon Network

-I watched it between 2008 and 2020 (I was born in 2004 so it was most likely 2010 - 2015, but I'm not 100% sure)

Show:

-2D Animated Show (most likely Anime)

-The characters collected monsters that had to be summoned from some object

-The main character was a boy

-there was also a girl character that had a very female looking monster (the monsters eyes were covered kinda like Gojo from Jujutsu Kaisen). It was basically a women

The two Episodes I remember:

Episode 1:

-The characters got a new monster (I think by solving / discovering) something in a cave

-The monster they found was called "Drei Helden" (translated from german that means "Three heroes") or something along those lines

-It was a group of 3 monsters that looked like Shovel knight, but with white armor and golden ornaments

Episode 2:

-this episode aired directly after the last one

-the protagonists had to battle antagonists that had 1 or 2 of some special kind of monster (like the legendary versions of the monsters. Each legendary had like a "type" / special "category")

-One of the monsters they had looked like a giant eyeball (kinda like the eye of Cthulhu but less veiny)

-They thought on (what I think was) a roof top and every think was pretty dark)

-In that fight the girls monster (with the covered eyes) sacrificed herself. (I dont know why, but I think that she couldn't be healed like normaly or something like that)

-they showed her damage through the thing that covered her eyes slowly breaking apart