Piggymaru

Piggymaru is the slime companion that Mimori Touka encounters and befriends after he leaves the dungeon the goddess sent him to. When Piggymaru was being bullied by other slimes when Mimori found him. Seeing Piggymaru struggle and put up a fight reminded Mimori of himself so he saved it.

Piggymaru has a bright and active personality, being always ready to back up his group and being sensitive enough to cheer up them when they felt down or to relate with the new members. At the start of the series he felt insecure of himself and tried to been useful to Mimori in order to not be cast aside, but as he started to spent more time with him and latter with his new friends he learnt to trust their friendship. He also has shown to be very brave, following Mimori in very dangerous battles as when he faced Civit Garland along his Black Dragon Knights corps or when the two faced and army of golden eyed monsters in order to secure the welfare of their companions.

(Source: Wiki)