What's the laws in ইসলাম to someone that really like to watch pornograpic (like hentai, ecchi, oppai, etc.)

It is completely Prohibited. Whether it be জীবন্ত অথবা not it is prohibited.
Allah says in the Quran: “And come not near to unlawful sexual intercourse. Verily, it is a faahishah (a great sin) and an evil way.” [al-Israa’ 17:32]
Is watching it not coming nearer to it?

Yes we have many Muslims who are watching this some know it is prohibited and some don't know.
One problem is ignorance, (I mean no offense to anyone)
But we don't understand the true consequences of what we are doing.
All this creates problems amongst the Muslims, so if one is addicted to watching pornography they should get help and ask Allah for help.
For Allah always উত্তর the prayer.
May Allah guide us all.