D rank= B rank dungeon divers
C rank= Apex B rank dungeon divers
B rank=apex A Rank dungeon divers
A Rank=Apex S rank dungeon divers
EX rank= World class dungeon divers
(Current summons Hajime has gained
Assassin- shuten-Douji (c-rank)
Archer- sei shounagon (a-rank)
AlterEgo- Larva/Tiamat (EX-rank)
Caster- tamamo no Mae (c-rank)
Ruler- Leonardo da Vinci (a-rank)
Berserker- minamoto no raikou (s-rank)
Lancer- artoria (s- rank bordering EX-rank)
Additional note: the summons will gain buffs based on the dungeons they are in, for example if raikou were to enter a demon based dungeon she gets a 70% damage reduction as well as a 70% damage increase.
There will be more summons as time goes on, but I'll have to divide them on rank.