 If you liked
Tenchi Muyou! GXP
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 ...then you might like
Isekai no Seikishi Monogatari
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+Also story plot of Tenchi
+Also Ecchi, Comedy , harem
+Also about a boy with a Women all around him
+Also about space, mecha, spaceships
All along anime is very similar , more or less have same Ecchi humor, same girls that are in love with he boy.
The most similar anime to Isekai no Seikishi Monogatari, firstly they are done by the same creators and they both are spin off from the Tenchis Original Series. But, besides that: They shares the same harem ending, they both have an amazing male leader who's been sexually harassed by the female leaders (mainly by one), we may say that Kenchi is far better than Seina, but they both rock.