Eric is the son of Tom, who is the brother of Jerry, who is the daughter of Sin. Doremon is the sister of Popoy, who is the son of Chain. Ivanka is the daughter of Popoy, who is the husband of Jerry. Sin is male and Chain is female. How is Ivanka related to Eric?

Introduction / Context:
This is a multi step blood relation puzzle involving three generations across two connected families. Such questions measure your ability to trace relations through several links and then compress that into a single common term such as cousin, aunt, nephew and so on. Visualising a family tree is the most effective way to solve these problems.

Given Data / Assumptions:

• Eric is the son of Tom.
• Tom is the brother of Jerry.
• Jerry is the daughter of Sin, and Sin is male.
• Popoy is the son of Chain, and Chain is female.
• Doremon is the sister of Popoy.
• Ivanka is the daughter of Popoy, who is the husband of Jerry. So Popoy and Jerry are married.
• Standard exam assumptions of monogamous families are used unless stated otherwise.

Concept / Approach:
The best approach is to build the family tree layer by layer. First build the Sin side of the family that contains Tom, Jerry and Eric. Then build the Chain side that contains Popoy, Doremon and Ivanka. Finally, connect both sides through the marriage of Popoy and Jerry and see how their child Ivanka is related to Eric, the son of Tom.

Step-by-Step Solution:
Step 1: From "Tom is the brother of Jerry" and "Jerry is the daughter of Sin", we know that Tom and Jerry are children of Sin. Sin is in the grandparent generation.Step 2: Eric is the son of Tom, so Eric is in the next generation below Tom and Jerry. Thus Sin is the grandfather of Eric.Step 3: On the other side, Popoy is the son of Chain, and Doremon is his sister, so both Popoy and Doremon are children of Chain.Step 4: Ivanka is the daughter of Popoy, who is the husband of Jerry. That means Popoy and Jerry are a married couple and Ivanka is their daughter. So Ivanka is also in the same generation as Eric.Step 5: Since Tom and Jerry are siblings, their children, Eric (child of Tom) and Ivanka (child of Jerry and Popoy), are grandchildren of the same grandparent Sin.Step 6: Children of siblings are called first cousins. Ivanka is female, so from Eric point of view she is his cousin sister.

Verification / Alternative check:
List generations clearly. Generation 1: Sin and Chain. Generation 2: Tom and Jerry (children of Sin), Popoy and Doremon (children of Chain). Generation 3: Eric (son of Tom) and Ivanka (daughter of Popoy and Jerry). Since Eric and Ivanka share one common grandparent Sin through their parents Tom and Jerry, they are first cousins. Gender only refines the term to cousin brother or cousin sister. Here Ivanka is female, so cousin sister fits.

Why Other Options Are Wrong:
Ivanka cannot be Eric daughter, because they are in the same generation and both are grandchildren of Sin. She is not his niece because she is not the child of Eric sibling. She is not his nephew, as that would require Ivanka to be male. The term cousin sister perfectly captures "daughter of my father or mother sibling" when that child is female.

Common Pitfalls:
Many learners get lost in the long wording and mix up spouses with siblings. A common error is to treat Popoy and Tom as brothers just because they appear alongside each other, which would completely change the relation. Always carefully mark who is whose parent, who is a sibling and who is a spouse. Drawing a simple tree with arrows for parent child and side links for marriage helps prevent such mistakes.

Final Answer:
Ivanka is Eric cousin sister.