Though it may seem like Eca's not the usual one to welcome a person with open arms, she's very respectable towards her friends. Those who understand Eca's opinions and beliefs are the ones she will consider to be her true allies (and not the ones she'll kill). To know that you've become a friend of Eca, she'll make sarcastic jokes around you, showing off her rather "softer" side. Funny part is that despite her intimidating look and with those piercing icy eyes, she's somewhat fairly easy to get along with. It will just take some time, in order for you to gain the assassin's trust.

Big tip: Talk about anything that seems "aesthetic", that'll get her attention. Mention anything that involves reading, time (especially), anything simple or something stupid (careful with that, nothing too ridiculous), you'll get her attention. By the way, don't expect the relationship to go any further than just friends. Eca doesn't plan to have any intimate relationships in her life since the thought of it disgusts her.

Pray that you're not a hunter and specifically, a vampire hunter. You'll automatically become Eca's enemy right then, and there. If you are said "hunter", consider this, you've become Eca's target. She will not hesitate to come and kill you, or even make you wait for your death with that pocketwatch of hers that she uses to taunt and time you. Aside from that though, it's a hit or miss with Eca to be her "enemy". If you're that extremely loud and obnoxious kind of person, you're a nuisance to her since she's one who prefers to be discreet. Also, if you disrespect her beliefs and her opinions of freedom for all the supernatural to run free without fear of death from hunters, say goodbye to trust.

It should be acknowledged that Eca can become very sassy, and predatorous. She can be also ignorant and ruthless, as well as she's very determined for one goal; to assassinate you.

You only just met Eca? Only talked with her a few times, had a dead-end with her, and nothing else? Well consider this, you're in this section meaning you're just someone she knows, someone she passed by with. It's not bad, at least you're not another target of hers that she can toy around with.