Cry has terrible luck. The absolute worst thing that can happen will always happen. It's almost like his words speak things into existence. There's an upcoming arc (the very next one after this one) where he's worried about the slime that was supposed to be in the capsule that he threw at the bosses a couple chapters ago - "Sytry's Slime". Because it wasn't in the capsule, he's super worried about where it could be, especially after he just dropped his really powerful sword just before reaching the boss fight (the sword that Liz handed to him last chapter).
When looking for this slime, he asks some teams in his clan to check out this treasure house and to "be careful of a slime, but not a normal slime". We obviously know that he's talking about Sytry's slime, but because his wording was a little more ambiguous, the real enemy that appears isn't that Sytry's slime, but another monster that has a body that looks like it's made of slime (although, for super spoilers, see below).
If you consider things like this to be common for Cry, then you can understand why his friends had to grow into such monsters just to be his friend - if he's constantly attracting the worst kind of monsters without meaning to, they have to be monsters themselves just to survive. And all those friends think that Cry has been trying to help them get stronger, so they're really appreciative of it.
An example of this: Later in the story, we learn that Cry usually has his sister charge all of his relics (of which he has hundreds), which uses up all her mana and basically makes her mana-drunk, but also increases her overall mana capacity because of the strain. He doesn't realize this is happening because she regards it as "training", so she never complains to him.