Rias

Weird btw... The creator himself cane out and said the "filler" episodes were all canon to the story. They where story beats he wanted to put into the manga but didn't have time to. It's actually referred to as anime canon.. In fact without said anime canon episodes. Most characters would be practically non existent. We would have little to no info on them nor emotional ties.

Something that's crucial for a shonen anime. Like HxH, DBZ, Bleach, Naruto/N. Shippuden, And others. They do so well with emotional moments. Because WE KNOW the side characters. We CARE about their issues. We know the main character values them. So we give them more value